It’s a little more disgusting than you’ve mentioned here.

There was one aspect of Siberian mushroom intoxication, reported even in the earliest sources, that must have seemed singularly shocking to one who encountered it for the first time—the drinking of the urine of a bemushroomed person, and also the urine of reindeer that had browsed—as reindeer apparently like to do—on the fly-agaric.

By no means all the tribes that used Amanita muscaria also drank fly-agaric urine, but the custom was sufficiently well-developed and widespread to have drawn the attention of almost every observer—from Count Filip Johann von Strahlenberg, a Swedish colonel who spent a dozen years in Siberia as a prisoner of war and reported on his observations in the early eighteenth century, to the trained ethnographers of the late nineteenth and early twentieth centuries, when the Europeanization of Siberia, which had begun in the seventeenth century, was well underway, but before traditional tribal life began to be radically transformed even in the remoter hinterlands in the aftermath of the Russian Revolution.

https://www.drugtimes.org/hallucinogens-culture/the-flyagaric-and-the-intoxicating-urine.html