The picture you see shows my filter housing, which contains a cartridge filter.
Last fall, a "pool school" guy came out to give some basic information.
If I recall correctly, one of the things he said was not to use the drain plug shown in the picture to drain water from the pool (the one that appears to me to have been put there for just that purpose). I'm not sure of his reason: I vaguely think it was because it wasn't supposed to be good for something (too much stress or pressure on the housing or pump perhaps? I don't know).
We get a lot of rain, and any other method I can think of for draining the pool after it overfills after a good downpour would be a lot more hassle than unscrewing that drain plug and turning on the pump.
1) Was the guy right or wrong?
2) If I do unscrew this plug to drain the pool, should I leave the return valve from the filter housing to the pool open or closed while draining?