Maybe the bottle they give her is like antifreeze or something? (I dont even know what that is, beyond the fact they put it in your car if its cold?)
Some of the aircraft we had, there were little acess panels below the sink, at floor level (right next to the door), where you could reach right in, around some pipes, and pull a little ring, and it would suck out all the gunk. It was a very awkward thing to do, as you had to be on your hands and knees on the galley floor. But, if someone made the mistake of putting something in there they shouldnt have, it worked very well.