Will your mom let you use the other bathroom in the meantime? This sounds like an awful thing to have to see and smell even once.

I don't think people stop drinking until they want to. Either something comes along that they care about more than drinking or bad things start to happen that make them reevaluate the need to drink. Or he could have a mental issue that needs to be addressed (but bad things happening sometimes make people realize this). I would ask him how he got home and encourage him to get a ride home or drink within walking distance.

I am sorry you are having to endure his bad, inescusable behavior.