I used it to "fix" and underground leak (elbow under my skimmer) a couple of year ago, this involved disconnecting my pump and temporarily capping off the suction line where it went below ground (rigged a temporary above ground line to the pump), lowered water level just below skimmer level, and rigged up a cheap sump style pump and bits of an old suction side cleaner hose to pressurize the line and force the marlig gunk out through the leak in the suction line. Let it sit for a day or two, repeat, and flush out the suction line before reconnecting the pool pump. All this effort bought me 2 years before the fitting failed completely and I had to cut out a 3x3 section of concrete decking and dig out under the skimmer to replace the elbow fitting. (pool builder used drain pipe street elbow, and had it in a bind, so over time the glue failed and eventually the fitting popped off the bottom of the skimmer, but that did take 35 years).