HMS Beagle wrote:
Most RV tanks are made of polyethylene. This is one of the "low surface reactivity" plastics that are very difficult to glue. Properly made tanks have welded or "spun in" threaded fittings to take the plumbing. I would not depend on hardware or RV store sealants to give you a lasting repair. I would find out what the factory used (recognizing that they may not have used the best methods either) and verify that it is recommended for use on polyethylene. Certainly ABS drain pipe glue will not bond to PE.
One thing that does work pretty well is West G-Flex epoxy. However to make it stick to PE you need to flame treat the surface. The West site has instructions on how to do this, it is simple to do but you may have access problems in your situation.
The pictures you posted almost looks like they used a poly urethane glue like Gorilla Glue. It foams like that as it absorbs moisture to cure. If so that's the wrong product in my opinion.
Thanks, you said it well, much better than I did... material limitations, thats why I'd use a mechanical (rubber) connection and clamps.