That is SO not kosher!
Despite being yellow, urine is categorized as being black water, meaning it's just brimming over with pathogens.
Grey water is what drains from your shower, sinks, and washing machine (if so equipped).
That's it.
Technically, if you're in the habit of pissing in the shower, it should be drained into the black tank.
Human urine is for the most part sterile. The exception would be someone with a urinary tract infection, and even those are considered non-contagious even with direct contact. There are no human pathogens that are transmittable through our urine. The sink and shower traps are going to harbor far worse bacteria than piss.
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