It's a triclosan one. I imagine flushing it all at once would be worse than using it.

Just put it in the garbage. As is, bottle closed.

Or save it for special occasions (which is what it was designed for). For example people are sick in the house, or you just cleaned out something really disgusting.

That was first question:

Have there been any studies on the bacterial resistance impact of EtOH gels? Natural selection will find a way to prevent cell membranes from being dissolved. Nature is a great hacker.

There have been extensive studies on the efficacy of EtOH hand gels - for a wide number of pathogens, they are just as, if not less effective than soap and water, especially when you add in mechanical action.

They're an excellent substitute, but not a stop-gap, especially not in the concentrations available through retail in the U.S.