On my boat, I have half inch water pipe made from a "plastic" and flexible material. Unfortunately, this is now outdated, with most boats now using 15mm flexible pipe. This presents problems with adapting the old to the new. Also, the fittings used to connect this pipe, (black elbow to left) are no longer available and sometimes come apart.
In New Zealand they have a 12.5mm pipe with push in fittings. You would think the half inch pipe might fit...., but no, it doesn't.
So here's how I have over come this problem...
Fortunately this plastic pipe is similar in size to copper half inch pipe and the compression fittings are available at most plumbing hardware stores.
To the right is a photo of old and new fittings used to attach to the faucet at the sink.
To the left is the new compression fitting disassembled. To the inside, is a rubber ring and star washer to grip the pipe.
Compare the above photo to the plastic one to the right. They work in a very similar fashion.
The fittings come in a number of arrangements. I bought a straight connector, a "T", and end threaded adapter.
To the right, the nut goes on first, then the star washer, followed by the rubber washer. Once the pipe is inserted into the fitting, the nut is screwed down to secure the pipe.
Now, the fitting, made for copper pipe, doesn't quite fit the plastic pipe, so a little modification has to be done.
First, use a dremel stone to slightly enlarge the hole in the center of the compression nut so that it slides over the plastic pipe. It only needs a "human hair" thickness taken off.
The pipe also has to fit the fitting. This requires a little sanding on the end so the pipe fits, snugly.
You can see that, in the photo to the right.
When assembling, slide the fitting onto the end of the pipe and mark with a felt pen. Slide off the fitting and then with the nut first, slide on the star washer with the points towards the yet to be fitted copper fitting. Slide this on till just past the pen line so that when the rubber washer is placed, it is is pushed on till just past the pen line.
To the right is the fitting about to have the nut screwed on to make the compression. Once that is done, regular plumbing fittings can be attached.
I've also had success with another type of compression fitting using a copper compression sleeve shown to the left. However, on occasion, some of these have leaked due to the copper sleeve not being perfectly aligned before compression. One has to remove a short piece of the pipe, (because the compressed sleeve is almost impossible to get off) and place a new compression sleeve on and make sure it is seated correctly before tightening up. It seems to me, the compression fitting with the rubber washer is a better fit and can be reused if one has to undo the nut.
Another method, show to the right is to get a hose tail with a plumbing threaded end, and attach with a suitable hose clip , or for a more secure fitting, use the wire tightener, and it's use can be viewed here