Last water

The Gemara in Cholin says that this is a law because of the salt of a sodomite. Although there are also other explanations. Some say that today, the salt of a sodomite does not fulfill this law, making it null and void (both opinions appear in the Shulchan Arash).
See review here:
https://he.wikipedia.org/wiki/%D7%9E%D7%99%D7%9D_%D7%90%D7%97%D7%A8%D7%95%D7%A0%D7%99%D7%9D