... believe it or not, I'm still getting work done on my boat. Anyway, I sealed the leaky cylinder up and installed a rubber ring on the piston and this mother pumps water. It is a respectable flow out of the garden hose. I emptied half a 5 gallon carboy in under one minute (I got tired). The only thing I noticed was a small amount of water worked its way past the piston and leaked out the open end of the cylinder; which would then drip back into the cockpit. Next thing is to build the teeter that my feet will push against.

That is a 3" shower gasket mounted around a little piece of Cedar and then sandwiched between a hardwood disk and the piston. It's screwed into a nut I epoxied into the piston. Petroleum jelly is the grease. The piston fits inside the PVC pipe and pulls in/pushes out water through the one-way valves at the end. Here's a sketch of the schema http://www.nwlink.com/~chips/paddles/images/footpump3.jpg