Its the renal system that filters out the toxins yet drinking piss is perfectly harmless.
Its harmless in the sense that its reasonably sterile – but having done the work of filtering out all those toxins drinking your piss just means your kidneys have to do that all over again.
Your poops isn’t so sterile as lot of the work of digestion is done by bacteria – a good proportion (almost of third) of the volume of your poop is actually bacteria, not old food, we get on quite happily with it them living in the gut, where they belong, but we wouldn’t fair so well rubbing them in our eyes or in open wounds. Its also not just the left overs from digestion, our liver, for instance, empties waste products from its processes into the gut as well – the brown-ness of your poop is largely from the liver breaking down old blood cells, so pale poops can be a sign of anaemia, but the liver is also removing toxins from the blood also, and again putting those back into your system just means having to work to filter them out again.