Sometimes you can do everything to keep your RV sewer system clean but inevitably it can start to smell. If your RV toilet smells like urine then it’s likely that the toilet bowl has urine on it. Especially if you don’t flush for number 1’s. Even if you do flush sometimes the water saving flushing can leave some areas of the bowl with urine on it. Luckily it’s easy enough to fix, simply use a bathroom cleaner and spray into the bowl every day. Or make sure that the hand sprayer is used to give the bowl a good rinse after urinating. If the smell is just urine then it’s unlikely that there is a problem with the black tank, as that would be a very different smell.  If you do think that there is a problem with your holding tank then an RV holding tank treatment should be used. This will dissolve the paper and waste and remove any blockages so that it can be emptied effectively. Always have an air freshener in your RV bathroom, to keep smells at bay.