Tub

Some people are taps
and their tub never empties.
Others are drains, they've no plug
and their tub's never full.

Two taps go together
like bathwater with bubbles.
Two drains are the same,
like a scrub goes with soap.

But nothing good comes 
from tap and drain together.
'cos the drain will never change
while the tap'll want the floor to be wetter.