Gregsnow, here is what I have found with my 222 livewell. If I pull the plug when the well is full and shut of the pump, the well will drain almost completely; just a little residual water in the bottom and not enough to cover the bottom. HOWEVER, if after it drains and I rinse it out with a freshwater hose which I usually do, a couple of inches of water will not drain out. What I do, is add enough water to get to about 3 inches or so above the drain, then the head pressure seems to start the siphon effect and it will drain completely. I just keep the hose running until water starts running out of the port side drain.
Also, if your livewell pump valve is open and you run the boat, you will get water in the livewell even though you don't have the pump turned on. Again, you might not have enough water in the well for it to drain, so try running the hose in it to get the water level up some. Or just turn on the pump and let it fill up a bit more.
You may also want to check your drain for obstructions too. I have had baitfish scales clog up mine and I've had to take a hose and force water through the drain to clear it.
Hope that makes sense and maybe it will help.