Yes, water weld is fish safe. people use it on their reefs for aquascaping, and i also have it in my pond, sealing a 4" pipe to the side of a plastic tote. works great.
Go to Harbor freight Tool store. Pick up a Plastic welding kit $20. This should do the job. Since it a rubbermaid plastic 55 gallon bin. Just clean it out and weld it. I welded hard pond liner, rubbermaid horse tank (tub) and even the blue plastic drum (barrel). It will work as good as new.
