Or sump, or pump-out, or whatever it's called - the pipe buried in gravel under the deep end of a pool which lets you pump out the ground water so the vinyl liner can be changed.
I'm pretty sure that the way my PB made one was to fasten some kind of plastic screen cloth over the end of a length of pipe and bury it in 3/4 washed gravel under the deep end. The gravel seems fine, but after some googling I'm worried about clogs. Should I ask him to dig it out and either drill holes or cut slits along more of the buried length to ensure that one misplaced chunk of clay can't render it useless? If he won't, is there any grave risk in going down there and doing it myself (after telling him I will, obviously)?