I've been building a livewell system for my jon boat. Everything at this point is cool but the big dilemma I can't figure out is how to rig the outflow on it.

Let's start with a diagram
http://www.calfishing.com/dc/user_files/4015-boat.jpg

So far I've rigged everything shown in the pic. The pump is mounted in a bracket on the outside of the transom. It has 3/4" tubing coming off it that runs up the transom then through a hole at the upper edge of the transom

On the inside of the boat I have a ball valve on the tubing to prevent water from being forced up the tube while the boat is underway (yes this is a not so thrilling feature of externally mounted centrifigul pumps). From the ball valve the tubing runs along the gunwale and into the cooler/livwell.

Where the tubing meets the cooler I have a threaded fitting so that the hose can be disconnected if I want to remove the cooler.

All of this works fine.

The REAL dilemma is how to do the drain on it. Before you rush to give me advice, consider the following factors...

The drain hose can't simply be hung off the side of the boat because the water level in the livewell is lower than the side of the boat. Therefore a hole must be drilled in the side of the boat.

Everything I've read about livewells suggest that you use a larger outflow than an inflow, ideally double the diameter (so 1 1/2").

The waterline on the boat changes depending on how many people are in it, if people are leaning to one side, and if the boat is underway. I plan to put the outflow toward the stern of the boat because this side will typically be the down side, however its very possible on this boat for the bow to be lower than the stern if I don't have the motor on the back and two guys are standing on the front or if I'm anchored from the stern and standing on the bow.

I'm also fixed on the location of the cooler in the boat. Yes I know it should be along the centerline of the boat, but that's just not reasonable the way the boat is laid out.

And I'd like to have it so that when the water drains out, it doesn't splash like a hose shooting into the water. I am thinking of some kind of tubing on the outside of the boat to force the water straight down into the water, underwater.

I may rig an additional drain hose on the actual drain at the bottom of the cooler that runs back to the drain plug on the boat so that at the end of the day I can open that valve and let water drain directly out the plug of the boat. That's last on the priority list right now though.

So I'd love to hear some suggestions on how to do this. And any tips on drilling 1 1/2" holes in aluminum boats as cleanly as possible. I looked at drill bits today and it looks like a hole cutter is the right thing to get but anyone who has experience doing this, I'd love to hear about it.