Plumbing – How to unscrew a broken washing machine filter cap

Mineral build up has likely cemented the aerator in place, so:

Wash off the WD40 residue with soap as best you can.

Get a glass or cup. Fill it with vinegar or a citric acid solution, and heat it in the microwave til hot. position the cup under the faucet so that the mineraled up threads are submerged. Let it sit for a few hours periodically warming the liquid and lightly tapping the aerator with a hammer so as to loosen residue. If you are persistent and lucky, the acid will dissolve the mineral buldup to the point you can unscrew the top half of the aerator.

If you have them, a mototool or detail sander might also be used to mechanically nudge the stuck threads. That'll open channels for the acid to get at the mineral buildup.

Well... you've got 22 gallons coming out of the washing machine each cycle. You've got about 2 1/2 gallons in the vertical pipe, and another gallon in the horizontal pipe, so you'd need to store another 20 gallons to be reasonably safe if you go down that route. I wouldn't advise it -- drain water has all sorts of junk in it.

Personally, I've never heard of a floor drain that is 2" or less, so your drain should have sufficient capacity to drain the water thrown off by the washer.

So it sounds like there's some back-pressure causing the water not to flow through the drain pipe as fast as it should. I'd start by snaking it, and if that doesn't work, I'd extend the PVC pipe through the hole and fairly far down the drain; this should reduce the pressure drop and force the water through the drain faster.