Main drain line leaks are a pro job.

Probably not. Unless you have a pressure test kit, a jackhammer, and experience with hydraulic cement, you’re looking at a bad time.

Main drain lines run under the pool shell. To fix a leak, you first need to find it — usually by pressure testing the line, which means plugging the drain at the pool and at the pump, then pressurizing with air or water and listening for bubbles. If it’s a crack in the pipe itself, you’re digging up concrete. If it’s a leak at the fitting, same deal. There is no easy above-ground fix.

Your options are: call a leak detection service (they have sonar and dye kits), then a pool plumber to cut and patch the line. Or reroute the main drain above ground if local code allows. Neither is a DIY weekend project.

This is one of those times where paying $800 to a pro is cheaper than the $2,000 in concrete repairs you’ll cause trying to save $800.