Tons of awesome information in here, now for my 2 cents about bilge pumps.
This was just screwing around in the bathtub to see what I could put together.
Parts
Two 1000gph Harbor Freight 12v bilge pumps
One Keene 2.5" Power nozzle
Two pairs of thick wire leads
One Craftsman 19.2v battery from my 1/2" impact
One Craftsman 14.4v battery from my drill
Some clear PVC hose and a PVC T and caps to join it all together
The suction was substantial and able to blow water out the back like a fire hose.
I have no idea how my gph the pumps had from overvolting to 14.4 and 19.2 volts and I don't know how long they would last, but pressure was increased quite a bit.
I should also mention that even though one was getting more power than the other, there was no blowback out of the 14.4 pump and was still bringing in a lot of water through the base.
Now its not gold but the nozzle picked up coins and bolts with ease in my highly scientific closed lab - The Bathroom.
If these pumps can handle 19.2v for any amount of time then it would be worth doing.
I was not able to do longer tests because the battery ran down pretty quickly and the pumps came through just fine.
Now being that we are generally the tinkering type, build them all.

I have been wanting to buy one of the Utility pumps for a while now.
I can say though, don't bother with trying to make your own power nozzle out of PVC, just buy the real deal and work around that.