Is pissing in an Olla a good idea? Pissing directly on the plants is no good but in an Olla the piss should be filtered allowing only the water out and if some ammonia gets through as well that's even better.

Eventually the urea will build up on the inner surface of the Olla preventing filtration and I'll have to dig it back up and give it a clean so the question is how much piss can terracotta filter?

I assume it should work fine, just like the sand filter in an aquaponics setup but slower. Bacteria will break down the urea into nitrates so you shouldn't have to worry about that. If I was to try it I'd go with plants that need a lot of nitrogen like potatoes or corn
