I have an odd problem. Essentially I am working on fabricating a connection between two fiberglass pipes that are intended to be submerged underwater (depth 30ft). No water should make it inside of the pipe so I need the connection to be waterproof. I am imagining something with an O-ring and a screw like mechanism (similar to a toy submarine) but I can't figure out how to create this or hack something together. The pipes have an outside diameter of 4.74 inches and there are no threads, just a straight cross section. I can't seem to find any sort of coupling with this weird diameter, and I'm not sure how I'd attach one if I did. Any advice?
You might try using a no hub plumbing connection, it's like a rubber pipe with a metal band around it. I'm not sure if they come in 4.75 diameter though.
something like this