That is fish abuse. The whole bathroom would stink if you didn't keep the tank clean. There does not look like there is a way to put a filter or aireator in there. It would be a constant problem. Also, there are two caps on the counter top that come off for feeding. *Any* soapy water that happened to drip in there would kill the fish immediately (soap is a surfactant that affects their gills, and they literally drown). Bad, bad idea. Bad idea. Can't tell you how bad an idea it is to have fish in your lavatory?