"The cause must lie elsewhere." This sort of statement insures you will never find the cause. It doesn't matter what you are trying to find. This is right up there with "the alternative is unthinkable." which was bandied about when all the financial firms were collapsing.. When I hear that, I think speak for yourself. Back to the subject at hand, why don't you get some of the pvc pipe, preferably from the same batch that was used in this construction, and soak it in some water from your inlet pipe? At the same time how about you get some of the material used to seal the junctions and soak that in water. Test both water baths periodically and see what happens. Of course one should have a control bath the same as the other two to see what happens when nothing is in the bath. After that report back and we'll tell you what to do next :)

Or conversely the non serious could just goto hell.

I don't get paid for it but I've coded quite a bit, currently spend about 10 hours per week. I consider it a hobby, Have a project I'm focused on, it's big it's bad, its ambitous, it will probably take me ten years to complete it :)