The average person flushes 1-2 liters of urine per day, probably without realizing that urine has been used to treat everything from basic infections to menopause.
For example, during WW11, newly discover penicillin was in short supply. But doctors realized that when someone took penicillin, anywhere from 40-99% of it was excreted into their urine unchanged. Doctors started collecting and crystalizing patient’s urine to extract the drug.
In another example, Bruno Lunenfeld, a medical student in the early 1960s, recognized that during menopause women’s urine was likely to contain high levels of the hormones that stimulate ovulation. His proposed drug, however, would require thousands of gallons of urine from menopausal women. Lunenfeld and the Catholic church struck a deal that gave the scientist access to urine from nuns living in Catholic retirement homes. In 1962, a woman treated by Lunenfeld with "Pergonal" gave birth to a baby girl, the first child born from the treatment. Pharma company Serono began to synthesize the hormones in labs and the resulting treatment, Gonal-f, was first approved in 1995. Serono was acquired in 2007 by Merck, which continues to produce the drug today.
For more on the historical usefulness of urine, check out this video by SciShow.