Are there any products on the market that will seal a leak in a 4 PVC main drain line on a gunite swimming pool?

go to your local roofer...larger scale and ask him for a peice of EPDM >45 mil roffing rubber big enough to wrap your leak with 2 times...use contact cement ond the COMPLETELY DRY pipe all the way around...and then the rubber....it will goe around 1 complete time then you will have to coat the rooing rubber with contact cement to get proper bend on the 2nd wrap....then use hose clamps to reinforce... A: And this is only a temporary patch. Supposing you did not prep the site well enough. Supposing the rubber had a defect in it. In some areas ground gophers could chew through the rubber or be attracted to it from the odor. Foolish idea - do the job right in the first place for peace of mind. Better yet let a professional do the work then it will be guaranteed or warranteed.