People used to use urine to tan animal skins, so families used to all pee in a pot and then once a day it was taken and sold to the tannery.
If you had to do this to survive you were "Piss Poor".
The really poor folk who couldn't even afford to buy a pot, "didn't have a pot to piss in".

And on the subject of animal skins, «bucks» as a slang term for dollars stems from the time when actual buckskins were used as currency for trading

The current day English word "impediment" derives from the Latin term "impedimenta" which originally referred to the gear and equipment Roman soldiers had to carry while on the march. Roman soldiers found it to be such an inconvenience and annoying responsibility that the meaning of the word eventually evolved to reflect that.

More stuff that I can add to my HUGE store of knowledge

That's really interesting to finally know where those phrases came from!