Eactly what RAP said and you could/should even take it a step further. Figure out where the last bit of water sits in your well when it's all but empty and there's your drain placement. On my last boat, I always had like a half gallon or so that wouldn't drain that drove me crazy!
RAP, don't they make a double-duty pump for washdown/livewell that's a little more simple than what I described?