True enough. And if I'd typed out my complete thought (what, you can't read my mind?) I'd have added that I'd then slap the rubber plug and Tape of Duct on the pump end. The poly would really just buy me some time to get the vac off and plug in place before too much water re-entered the drain. Kind of a cheapo one-way valve, albeit a leaky one.

Needed would be a ring-type affair to fix to the end of the telescoping pole larger than the drain, bent at an angle to press the poly onto the drain as the vac was turned off (and a wife with a good sense of humor, which I have). Got an old skimming net that I'll sacrifice.