My guess is that you'd tire of this fairly quickly. I'd be easier to go to your funnel approach. I'd use one of those large funnels with the long flexible spout.Now, the apartment is on the second floor. Assuming the pipe runs straight down at least a couple feet, one could possibly stuff one of those check-valve-ended quick-siphon hoses down the pipe low enough to simply start a siphon.
I'm not sure that a pump would preclude tooth brushing or shaving. Certainly a sump type pump would not. But I agree that gravity feed is best (gravity hasn't failed us for many, many years ). But, even without a trap under the sink, it likely would raise the sink up high. If not too high, that's the way to go.I think gravity feed is the way to go. If I get a pump like that I can never brush my teeth or shave in the sink, which I may want to do, having only one each of wife and bathroom. It's true that the sink will be inconveniently high, but at least I'm tall.