BUT THEN YOU HAVE A SHIT WATER DRIPPING PIECE OF PLASTIC I AM NOT AMUSED
No, because the only way for the water to touch the plastic is for it to already be overflowing. This traps a layer of air between the plastic and the water creating a section. So when you push the air down, it’s forcing the water through the pipes. This is actually really cool!
Arthur Weasley is so proud of you, Japan. Countering a regurgitating toilet spell with a simple sheet of plastic.