Did you ever wonder where this came from?

[Jemisa]

They used to use urine to tan animal skins, so families used to all pee in a pot & then once a day it was taken & sold to the tannery.......if you had to do this to survive you were "Fosters Poor"
But worse than that were the really poor folk who couldnt even afford to buy a pot...........they "didnt have a pot to Fosters in" & were the lowest of the low

jem

[Stephen_G]

They also used the stale urine in the manufacture of tweed.

[Jemisa]

That should be "a pot to p!ss in"

jem (thanks ed)

[Hopkirk]

The Amber nectar?