Holding Tank Modifications using Polyethylene Pipe

More work to my holding tanks! I alluded to some of the benefits of using polyethylene hose for sanitation hose and you can read about it here.

 The first thing I did was remove the input hose and fitting, to the holding tank which was located on the side of the tank. Last year, I had relocated the tank air vent to the top and did a temporary block off, of the old side air vent. You can read about that here. That was located just above and to the side of this fitting seen to the left. I used a Dremel and hacksaw to make the cut of the bronze fitting.

 I prepped the area to get ready to epoxy glue on a cover over the old fittings. Old paint removed and each opening stuffed with toilet paper so that the glue would not full into the tank. The glue is made from two pot epoxy (slow set) with silica powder/binder added until you get the consistency of thick peanut butter.

 To the left is the finished fibreglass plate epoxied to the tank. This year I decided to use some off cuts of fibreglass which are cut out when the boats are removed from the molds. Typically, they are window cutouts and hatch cutouts which are then discarded. You local fibreglass boat builder will have plenty of these to give away.

In preparation for the top fitting, I found the best location; drilled my hole for the polyethylene through hole; and then sanded the area for gluing the fibreglass plate to the tank.

To the left is the finished fitting. You might notice that the black hose it is attached to is polyethylene pipe.
Polyethylene pipe is NOT as flexible as sanitation hose, so you may have to use elbows etc to get it to go where you want to. You can also use boiling water to get a little more curve from the pipe.

To the right you can see the 25mm polyethylene pipe running down and through the wall where it goes to the macerator pump. The bigger 38mm (inch and a half) pipe runs from the bottom of the tank to the "Y" valve and then the polyethylene pipe continues on to the pump out pump. A diaphragm pump with joker valves each end.
Now the outflow is of poor design and should never come from the bottom of the tank, other than a drop down pipe inside the tank, from the top. This is due to the fact that effluent is always in the outflow pipe which leads to permeation  I'm using polyethylene pipe from the bottom of the tank and feel confident, there will be no permeation.

Above you can see I used barrel nuts. This makes presenting pipes up to the fittings real easy. In this case I didn't need to use them, but I had bought them with me, so decided to use them.
To the left you can see the macerator pump with barrel nut fittings at both the inlet and outlet. The outlet has a PVC type which was fitted some time ago. On the other side of the barrel nut, I have a joker valve inside the other half of the PVC barrel nut and then a valve. This is because it is pumping up hill and one day I may need to service.
I have now added a polyethylene barrel nut at the inlet side. Also, but not shown, is a threaded pipe (at the inlet side before the barrel nut), which goes to a valve, before joining up with the 38mm pipe from the toilet bowel. IF the pump needs servicing, I just
turn off the valves at either side of the pump; undo the barrel nuts (usually by hand); disconnect power; and pull the pump out. I have a few "boat towels" to mop up the small amount of fluid that will spill.
And let me say, the area smells so much better already. I might even replace the deck pump out hose ( which goes to the "Y" valve. But my wife says, that is just looking for work. Maybe if I get bored sailing?
Listening to "Just Waiting on a Friend" by the Rolling Stones.

Replaceing Sanitation Hose

Some of you may have experienced the "smelly" boat syndrome, and a lot of the time this often points to the sanitation hose which is permeating the smell, from the contents inside the hose.

Analysis and Design
When sanitation system odors end up on the wrong side of the hoses and tanks that are designed to contain them, the most frequent analysis is, “they are permeated” and a lot of the experts call for wholesale hose replacement. In fact, while this may ultimately be necessary, it’s often a case of addressing the symptom rather than the cause. If the hoses are replaced and the design is flawed, then it’s likely the new hoses will, once again, fail or permeate prematurely. (see avoiding sanitation woes)

How do you test for permeated hose? Once you have eliminated all other sources for the odour, take a flannel and soak it in hot water. Ring it out and drape over the suspect hose for a few minutes. Then take the flannel and place in a zip lock bag and take outside to fresh air. Open the zip lock bag and smell. If you smell sewage, then you hose is permeated.

Before I begin with my solution(s), I just want to recap some of the salient points for a healthy head/holding tank systems and things you should look at on your boats sanitation system. By ensuring these procedures and implementing the points below on design layout, they can greatly reduce the the permeated hose problem.

• Rinse the holding tank out before layup and after every pump out. Lots of H2O helps with cleaning the remainder of the "solids" which tend to fall to the bottom of the tank and build up.
• If the holding tank has an inspection port, use that to wash down the sides of the tank; but watch for splatter back!!
• What sort of tank should I have? I prefer polyethylene tanks. The holding tank in many boats is constructed of low density polyethylene, heat welded from flat sheet with polyethylene fittings. Not much can go wrong as polyethylene does not corrode, is impervious to odour and has great impact resistance. Fiberglass would be my second choice. Metal tanks are a poor choice due to corrosion.
• Next step is to check the other components, Y valve,  macerator pump, hoses, hose clamps, tightness of joints, and vent line. Two outlets can prevent the need for a Y valve.
• Flow into the tank from the head should be on top of the tank This will depend on your location of the tank, but if attached to the side, slosh from a boat heeling can back flow down the delivery hose and becomes the standing waste inside the hose. It also allows you to disconnect the hoses from the fittings if the tank is near full
• The air vent should also be at the top of the tank and as large as practicably possible. Better still, put two vent hoses on to allow for a cross flow of air inside the tank. Aerobic bugs don't make the stink. Anaerobic bugs are responsible for the sewer smell.
• The discharge line should also come from the top of the tank with a drop pipe. It is a poor design when the discharge is from a fitting at the bottom, or lower side of the tank and this leads to the hoses continuously submerged in effluent.
• All hoses should run "down hill" or free draining to prevent standing effluent. When hoses are installed with large dips, low spots, or "u" shaped bends, effluent will settle in those bends, and it will be a challenge for even the best permeation resistant sanitation hose. These low spots can also lead to clogging.

This is all in an ideal world where holding tanks are designed properly, made from the correct material, plumbed correctly and the sanitation hose is the best money can buy. It doesn't happen. For instance, the holding tank location is often decided by what space is available. This often leads to hoses being plumbed that have residual effluent sitting in the hose. Sewage allowed to sit in the hose develops acids and gas that shorten its odor-free life. This is especially the case with white vinyl extra heavy-duty sanitation hose. Good installations are short and self- draining (no kinks, loops, or dips), with tight connections. Overtight fittings and clamping can damage hose ends, causing leaks and odors. On my boat, the tank is higher than my head and the toilet has to pump up hill to the holding tank. Without extra flushing, this leads to effluent sitting in the hose. This also true of my discharge line.

To the left is a quick drawing of my head and the associated items in the sanitation circuit. There are a number of problems with my system.

1. From the Macerator pump, it pumps up hill to the tank and if not flushed sufficiently, effluent stays in the line.
2. The intake to the holding tank is on the side and should be on the top
3. The outflow from the tank is from the bottom and therefore effluent will sit in the hose from the outlet to the Diaphragm Pump. A better option would be to have the outlet from the top of the holding tank with a drop pipe inside to the bottom for pick up 

So because of these poor designs in my sanitation system, effluent eventually permeates the sanitation hose and the boat becomes smelly. We all know how hard (and messy) it can be to change that sanitation hose and I have two ideas which may help with that. In addition, next time I'm at the boat, I will be changing the intake on the side of the holding tank, to the top of the tank.

First is to use barrel connectors made for alkathene (MDPE) pipe at each end of the sanitation hose. I use Hansen fittings. They may be called something different in your part of the world, but are commonly found in the farming industry and the marine industry. Our local chandler has sold these for years, but I never knew about the barrel fitting until I visited a more extensive store dedicated to Hanson fittings.

Barrel connector = big Nut

The picture to the left shows a barrel connector, which is the big nut in the middle. With one of these at each end and the sanitation hose between, one simply undoes the nut and pull the whole hose out to replace it.

Barrel nut  in the picture to the right undone. The big nut turns and slides back to allow the male end to slide out side ways.

Barrel nut in picture to the left showing the "O" ring which sits across the face of the opposite side for sealing.

Hanson makes hose tails, but I prefer to make my own.  They are good for tight/short runs of hose, Take a 1 and 1/4 inch nipple and turn one end down to 38mm. It just takes the threads off and I find the hose is a better fit and easier to get on and off. One and a half inch sanitation hose fits really good with a hose clip. One can also use the Hanson threaded end to pipe fitting (male straight coupling), by unscrewing the locking nut and discarding it, and slide the sanitation hose on and secure with hose clamps. If using Akathene pipe as suggested below, then you slide the pipe onto the tail and screw the nut over the pipe which cinches it down onto the tail of the fitting.

An image of one is shown below.

The other idea, of which I'm going to try out, is to use Alkathene (MDPE) pipe. This is a flexible pipe made from Polyethylene and I'll be using a medium density pipe. I'm trying it out because there is no info or data of anyone ever using this type of hose for boat sanitation hose. And yet it makes sense to me.This material is the same stuff that holding tanks are made from, and is used for effluent in our cities main sewer system and used by farmers for effluent discharge. While the stuff I will be using is designed for the transport of water, it is made from the same stuff the effluent MDPE pipe is, but at a size I can use. i.e. One and a half inches and one inch. (25 and 38mm)

Be aware that the pipe comes in low density and ranges through several levels to high density. It also comes in a range of sizes. The 40mm pipe and fittings are the one and a half inch  variety and in fact the inside of the pipe (ID) and  outside of the tails measure 38mm. This is the "real" size.

I'm setting this up so that, if I'm not happy with the Alkathene pipe, I can revert back to the sanitation hose without much ado. But I'm confident it will stop the permeation woes. The MDPE pipe is not as flexible as sanitation hose and if working with tight bends, you may have to use a Hanson elbow to get it around a corner. It is however, flexible , resistant to cracking, corrosion resistant  (some sanitation hose has a metal coil within the walls),chemical and abrasion resistant, excellent pressure resistance, easy to install, and more flexible than HDPE pipe. I have also used it around my farm, and it is so easy to connect, a child could do it.

While I would like the discharge line from the holding tank to come from the top of the tank, I'm going to leave it for the time being at the bottom of the tank. I'm hoping that by using MDPE pipe, which should be as good as any holding tank made from PE, then the issue of effluent in the line will not be a problem.

I also acknowledge that if you are using sanitation hose with barrel connectors each end, that they then in turn have to be connected to your devices. If your devices don't have a screw in fitting (like most PE holding tanks do),and has hose tails only, then one is faced with extra hose and hose clamps at each end. I think this is worth the extra "risk", and if the hose tail off the barrel connector is kept close to (<1/8 inch) from your device hose tail, then permeation at those points would be minimal.

Another change which I will also be doing is to put a barrel nut either side of the macerator pump, so that it is easy to take out should I need to work on it. It's in a tight location at the moment and difficult to get at the pump. These barrel nuts will make taking out the pump so much easier. I already have one on the discharge side of the macerator pump with a non return valve ( a joker valve, by which I machined  the barrel coupling to take), and a shut off valve so that if taking the pump out, I don't get a back flow from the hose leading up to the intake of the holding tank.

Below are some photo's showing the ease of the barrel nut disconnect, using both sanitation hose (in white) and Alkathene (MDPE) pipe in black.

You can place the nut of the barrel nut so that either stays on the removed hose section, or stays at the appliance fitting end.

Hope this will help for your next change of your sanitation hose. Below are some links that I thought might help.

Here is a list of Hanson couplings.

A comparison of Trident Sanitation hose.

Here is some instructions for installing sanitation hose.

Need a custom made holding tank. In our city one of the plastic tank manufacturers will make custom tanks on any shape you give them. It seems Raritan also does this. Check out your local area; there may be someone who makes PE tanks.

New Holding Tank Vent Outlet

On my forward holding tank, the vent line comes out the side of the tank, and because of the small size (<1/4inch) of  the screw in fitting, occassionally becomes blocked. In clearing that blockage last year, I noticed the thread for the elbow, that screws into the tank was stripped. At the time, I secured it back into the tank with my favorite 3M 4200.
This year was the time, to replace that fitting. It was very difficult to get at, being close to the side of the hull, and I didn't want to take the whole tank out to replace it. So I came up with this idea.

I used a plastic fuel tank through hull vent that comes in two pieces. I mounted this on a 1/2 inch plywood disc, coated with 3-4 coats of epoxy. The vent has a tube within a tube and when mounted with the hose tail pointing down , gives an extra protection from water ingress (like a trap). The curved "outer" vent entry has a stainless mesh which I removed. These features, when applied to the holding tank application, should prevent fluid escaping out the vent line.

Diassembled vent and mounting disk.

The disk was located on the top of the tank and the process for attaching with epoxy glue was the same as in this blog here.  Essentially I drilled a hole big enough for the vent intake; sanded the tank and mounting disk; and applied a epoxy mixed with a silica "glue" as a paste between both parts and allowed it to set up. The vent intake was a firm fit in the mounting plate and allowed for the removal (unscrews) of the bigger vent "trap" with hose tail; and also allowed for orientation by turning the vent intake to accommodate.

Finish product

The photo to the right shows the finished product, albeit that I don't have the right type of hose. I have 5/8inch sanitation hose coming from the USA. It's not a size readily available here.
The old vent hole was closed off using a plug they use on hydraulic items. I had one come off a new transmission cooler that was the right size. And of course to keep it in there, I used my favorite product, 3M 4200. One day the tank may be removed and that will be the time to remove the old brass fitting epoxied into the tank.

You might notice the inlet to the holding tank is also on the side, (under the old vent line). I don't under stand why they were built that way. Both the vent and the inlet should be on the highest point of the tank. Next year, I might move the inlet to the top of the tank. And that will give me a couple of more flushes. Doesn't a flush beat a full house?

Holding Tank Level Monitor

 I wrote previously about Gobius Tank Level monitoring. You can review that blog here.
On my forward holding tank, there is no way to easily place an inspection hatch for level monitoring (as per my previous blog). That is because to get at the tank, I have to remove a heavy mattress and covering board to see the tank. We also use the forward berth a lot, to store our extra equipment and sometimes supplies. So it can be a real hassle getting to the forward tank.
We use to empty the forward tank whenever we emptied the aft tank; but that was a
waste of tank treatment if the tank was say only 1/4 full.
So for me the solution lay with this new tank monitor device. You can see in the three photo's, the installation of the three main components of the device. The level indicator was placed just over the head electrical switch. The "computer" was placed on the side of a locker, next to the holding tank and the sender unit on the side of the tank as indicated in their web site tank calculator. Everything was easy except the sender unit. I followed their direction to the letter, but it would not stick. Sanded level, made sure tank surface was above 20 degrees C, and wiped surface prior with their special towel. Didn't stick! They supplied a spare sticky patch with the kit, so I tried the spare. Still no stick! So I wrote to their support email and two days later got a reply. The insinuation was that I had not followed with their directions

but they would post a new sticky patch out to me. Well, that wasn't going to help much, being on a boat, "cruising the world". So I took matters into my own hand. This they didn't recommend, but I did it anyway. I sanded the sticky patch that wouldn't stick so that it had a rough surface. Next I applied a very thin layer of 3M 4200 and applied the sender unit to the tank. I had duct tape ready to tape this unit to the tank until the 4200 set up. Next morning, the sender unit was attached "rock solid" to the tank. I proceeded to change the default settings and calibrate the unit as per their directions. And the unit works great. I may at a later date put a buzzer in the analog circuit which is detailed in their instructions. In the mean time, the 3/4 warning light comes on when the tank is 3/4 full. You can add extra sender units to have a 1/4 and 1/2 level light as well, but I'm very happy with this at the moment.

Holding Tank Level Inspection Window

I have a holding tank gauge with sender unit for some years now, but have never enjoyed removing the tank sender unit for a clean from time to time. Even when the unit is especially designed for black water, it would eventually clog up and need to be cleaned. My aft holding tank was easily accessible, so I decided to put a view port in so as to "see" the level of the tank. You can view the old sender unit here at WEMAUSA. It is the one on the right.
First, I had to design my window and decided for simplicity sake, to use a beckson hatch with a clear screw lid. These have a "O" rind for sealing. To this I mounted it on a half inch piece of ply cut to shape and given 3-4 coats of clear epoxy. Screws were mounted so as not to protrude through the other side. I also didn't want screws to go through into the holding tank and the mounting wooden plate adds some stiffness to the tank. Why wood instead of GRP? I like the idea of being able to reverse anything I do and the wooden base plate would (no pun intended) be easier to cut off.

After removing the sender unit, which was now showing signs of corrosion, I had to remove the screw in adaptor. This had a "C" shaped backing plate, so I lassoed it with a cable tie before undoing the last screw which held it there. I was then able to remove the backing plate with some ease.

I marked out the location of the new base plate, takeing out the old hole. But it was somewhat off centre, so to help with the hole saw, I screwed on a scape piece of wood and held it in place with screws through the piece of GRP that was going to be discarded.

To the right you can see how easy it is to drill a new hole where an old hole already exists.

Next, I sanded the paint off with a Rolok sanding disk.

The back of the backing plate was also sanded. Then I mixed up some epoxy with a silica type "Glue" additive to give a peanut butter viscosity. This was applied to the tank and then the backing plate pressed into the mix. Some squeezed out to the inside and I was able to get this before it fell into the tank. (wearing rubber gloves). The out side was smooth filleted with just a finger and left to harden overnight.

Finally the beckson hatch was bedded with 3M 4200 to the base plate.
And the finished inspection/view hatch to the left. It helps to shine a small flashlight up to one side of the clear hatch to get a better view of the level. Plus, now if I want to, I can put a hose in the tank to give it a wash out from time to time.

Sump Box for the Bilge

The people over at Carbo Rico_Tiburon36 have built a very nice sump box here's how they did it..........
I needed to add a separate sump to our grey water system. I have a store bought sump from Rule in the forward end of the bilge for the head and shower, but needed one to handle everything else including it. At a $100 bucks or more for one of these plastic boxes, I figured I could make one for a lot less.
Here is how I did it. You can build one too. It's fairly simple. I must add I had some scrap Plexiglas already. I bought the 500 gph bilge pump on ebay. The rest was scrap pieces of marine plywood.

Box measure 11x11x6 inches. It is 1/2 inch ply with 3/4 x 1 inch around the inside for a lip to help seal it and give a place to mount the bolts. The plastic screen inside is actually from a craft store. It is used for some kind of needle work.

Build the box. Then give it several coats of thinned epoxy inside and out. Save money, Don't buy CPES epoxy, just cut your already mixed epoxy with some MEK (NOT MEKP), thin till it's just a little thicker than water, almost half and half mix. MEK is just like Acetone, but evaporates much slower. Let it cure between coats, but put the first 2 coats on while still green. Sand for the last coat and thin it only a little or maybe not at all. You'll know you have enough coats when it is very shiny when finished.

Side note; this little trick will help you fix rotted post and the like without buying special epoxy. I actually apply it to porch post and columns before installing them. Then they never rot.

I used 1/4 inch bolts for the lid. Insert them as you make the box.

From Sump

Fit Plexiglas lid.

From Sump

Install pump and float switch.

From Sump

Install all the fittings in the box and screen plus the fuse holder outside.

From Sump

From Sump

Then install it. I eliminated 12 thru hulls with these two sumps. Now I only have 3 thru hulls.
I mounted it to the bilge with some stainless brackets I had. Screw them to the side of the box, make some pads that can be epoxied to the bilge , with bolts so that the whole thing is removable.
It is under the engine, but hopefully it will be somewhat accessible.

Holding Tank Tanksaver

While pumping out my holding tank, I heard a crackling sound of fiberglass. Stopping the pump out, I noticed the holding tank was starting to implode and the fault was a blocked vent line. To prevent a disaster happening in the future, I installed two Tanksavers from Sealand. These offer a one way valve which will open if it detects too much vacuum inside the tank. With those big dockside suction units, this could be the one thing that could save your tanks.


A three inch hole saw and a Tanksaver kit from sealand costing about $20 is required.

 Find a flat surface on your holding tank top surface and drill the 3 inch hole. Push in the rubber ring and then coat the valve insert with dish washing liquid and push in. That's all there is to it. Just a ten minute job on each tank.

Hole drilled and rubber insert placed

Finished product