Just a thought, PVC is going to deteriorate when the plasticisers leech out (I suppose sewage and cleaning
chemicals can be aggressive with this).
Well I used to do a lot of fly fishing
(bear with me), and fly lines used to suffer from quite rapid loss of plasticiser.
So I used to buy bottles of plasticiser to treat the fly lines with, to prevent this (some fly lines can be very expensive, and I never had to replace one when using this plasticiser regularly).
There could be a chance that cleaning
the outside of the pipes and then wiping over with a coating of plasticiser, might dramatically extend the life of the pipes?
This stuff is very cheap
, and it may be a worthwhile (though long term I suppose) experiment
I'll try and remember to do mine with it when I get the boat, and see how things pan out.
Another thought with combatting permeability. There's a marine version of the silicone polish for cars (Diamond finish one used be described as providing). The Marine version I used (on a couple of old boats) was extremely hard wearing in a marine environment
, and, as I used to sell uPVC fascias, etc (for houses), they suffered from having a very soft outer shell (it is disastrous to clean them by rubbing, as they get micro scratches in the surface and soon look a mess). So I used to recommend to customers that they gave their new uPVC a hard shell coating with this liquid silicone polish, as soon as the protective sheeting was peeled off their new installation
(uPVC conservatories too). After, to clean just hose them off. My father's place was treated this way when he had new uPVC fitted, over 22 years ago, and his fascias, etc., look like new today.
So you could plug
up one end of new pipes before fitting, pour some silicone hard shell polish into the pipe, plug
the other end, and swoosh it around inside the pipe so all surfaces get a coating? eta: Though make sure you rough up any outside areas you need to glue, so it doesn't prevent adhesion.
I am pretty sure it would be a great barrier to help prevent plasticiser leeching from the inside, and as it is a smooth, hard, shiny surface, should help prevent any icky stuff/crystals getting a grip inside, as well as help prevent smell permeability?