I water tested the silicon patch. It is not bonding only to the surface. The wall is nearly an inch thick, and is not smooth inside the hole, so it has alot more to grip onto than the plastic wall. I will see how it works for now, and probably change it out after a batch or two. I was considering just getting a stainless bolt, 2 washers, and silicon orings, and using that as a plug, that I know will last.