Piss or get off the pot

does anyone know the origin of piss or get off the pot

Families would keep a receptacle or "pot" available for urination and if someone were taking too much time at the "pot" then another family member would utter your phrase at the offender.

I believe the original saying was "****, or get off the pot". Before the advent of bathrooms and indoor toilets, a pot or "po" was placed in a room or beneath the bed at night and emptied in the morning. If someone really had to "go" and someone else was using the pot... then the utterance