Urine isn't really an avenue for toxin release ... that takes place more through the liver, colon, skin, breath, possibly feet...
So as far as that is concerned, I wouldn't really worry about it.
Other things can pass through the urine though, from the food itself. I don't know anything about Reishi mushrooms, so you might want to look into whether there would be any serious problem from "recycling" certain aspects of it. Is it something that can cause problems when taken in larger amounts? (although the amount passed through the urine isn't going to be all that much). Or is it something you can just eat normally and not worry about any side effects?
Generally, most herbal or natural foods should be fine though. Except maybe "poisonous" / toxic plants, but even those might not cause any problems as far as the urine is concerned...