My ex-wife, 55 years ago, squishing the heel of her hand into the bathtub drain: "Oh, because it makes the water go out faster." (she was a brilliant scholar otherwise)

If the outlet pipe is partially blocked by some soft gunge, squishing the heel of the hand into the bathtub drain might have the effect of a makeshift plunger and, indeed, help the water go out faster.

Perhaps she was more brilliant than you realised.


DC