Jeff, mine is a v-drive, but...
The boat's got to be on a real slope, like on the launch ramp, for water to exit the garboard drain (in the transom). Since you don't usually pull the plug till it's up in the cleanup area, there's always a bit of water still in there. In other words, when the trailer's parked on level ground, water collects in the bilge next to the driver's feet. I've gotten in the habit up bringing the wet/dry vac in and sucking the water out of there before wrapping her up. A little water does collect in between the liner and hull, too so it's good to let the vac suck for a minute or so.
I thought about installing a dripless packing, but that wouldn't help so much: our ice chest drains into the bilge.
As far as the pump goes: it might not be able to suck all the water, but if you see it try, and if it ejects even a little spurt, it's probably good to go. You could try bilge cleaner, but it seems to be overkill to me.
Oh yeah, almost forgot: the steering cable is run under the fuel tank (at least in the v-drives), and when I took my tank out, there was a collection of debris which was helping to trap water in there - made it even harder for water to drain out the back. You d-drive guys are in a little different boat (
) cuz you have a drain plug right under the engine too, right?
