I pee in the shower, it's basically going down the drain anyway. it's not that gross, it's just pee. After all, the dirt, sweat and other bodily/non bodily substances clinging to your person goes on the floor too, I see no harm in adding a bit of dirt if there's shampoo going over it anyway. showers are meant to clean (and relax, I do love me some peace and quiet in the shower, water trickling away in the absence of light.), and no one is ever clean going in.Most of the pee gets washed away, and what remains is just as dirty as the bit of dirt, the remains of shampoo etc.
Peeing in a bath is only acceptable if you then leave the bath, sitting in soiled water is kinda gross, seeing as long term exposure to pee makes you a raging mutant, and the only cure for that is a banana. *ahem*
seriously, don't pee in a bath you have to sit in.
(I thought taking a shower is more common than taking a bath, it seems a lot of people are talking about bath. do you have them together? in this house they are separate, mhh. This is intriguing. Cleansing rituals.)