For poly type tanks, better to use a glue formulated for the tank material. Marinetex makes Flex Set
which is labelled to bond PVC, ABS, Starboard, polyethylene, Hypalon, polyurethane, glass, metal, acrylic, fiberglass, polycarbonate, wood & dissimilar materials, as well as resist vibration, bending & shock. Its a two part epoxy formulation. I've used it to repair poly water tank leaks with good success.
I can imagine the PITA of hauling out the tank, but repair again may be the best option. IIWMI'd cut an access hole in the top of the tank to patch it from both the inside & outside (then patch the access closed obviously). I'd also reinforce the leak with a patch, probably one inside & one outside due to the overhead of the task, tho I don't have a recommendation of material for the patch.