Adhesive to bond polyethylene flange to fiberglass tank
I'm working on my Cayo C-11. The blackwater tank on these is made of fiberglass and is notorious for developing leaks over time. Mine has already been repaired once, by a previous owner.
The repair involved, among other things, replacement of the outlet flange with a piece that appears to be made of polyethylene. This is a poor choice of materials because of the difficulty of bonding polyethylene to fiberglass (or, for that matter, much of anything else besides other pieces of polyethylene) and because of the cold flow problems posed by this material. The flange is only partly surrounded by fiberglass and epoxy.
Predictably, the epoxy holding the flange to the fiberglass portion of the tank has given way leading to a crack and an odoriferous drip.
Here are the alternatives as I see them:
1) Remove the tank, cut out the flange, and glass in a new flange using PbearSailor's excellent photo essay on this sort of thing as a guide. I haven't done any fiberglass work myself in the past, and removing the tank is an involved process, so this is a last resort. Chemical prices being what they are this would involve over $100 worth of marine epoxy and another $100 of glass mat, mixing, handling, and safety materials.
2) Clean the exterior of the joint and carefully sand it down to a rough surface, and apply a specialty structural adhesive intended for polyethylene. I'm looking at 3M DP-8010, which is expensive but appears to be the only thing that will work. The adhesive itself is $40 for a 35 mL syringe, and the application gun, plunger, and nozzle are another $150 or so.
3) Duct tape and gorilla glue.