[Fishfirst]

The problem is that the fish have no shelter, usually one side is covered. And you can't use soap or brush teeth in a sink like this

I highly doubt the sink water drains into a fishtank like this. I think it probably drains into an actual drain and not the tank, leaving the tank water seperate from the waste water. If it does have the ability for the top to come off there is a possibility for it to work IF you can get cords in and out of the tank for an in tank filter/cirulation, and its not entirely sealed off from all oxygen.