Urine

A suprisingly useful aqueous mixture of several compounds.

Production

Production of urine is a natural process for most animals.

The major products of interest derived from human urine are:

Water
Urea, approximately 9.3g (0.66 mol) per liter.
Salt 3g per liter
Phosphorus, 0.4 to 1.0 grams (0.013-0.32 mol) per liter.
NB: 85% phosphoric acid is 15.2 molar, so between 500 and 1200L of urine would be required to make 1L of that acid.

Other animals' urine may also include:

In the ammonia production from urine process, it is of value to maxiomize the urea content of urine. Simple ways to do this include:

Collect urine first thing in the morning - urea is produced during the night, but is not diluted by additional water (not) consumed while you sleep.
Collect urine within 36 hours of heavy excercise
Collect urine from humans eating large amounts of protein rather than carbohydrates.

Obviously all of these could be done simultaneously, given the right diet, excercise, and sleeping schedule.