I have previously detailed the installation of an electric bilge pump.
Here I am depicting an alternative: a foot pump.
Greg Schwarz is a master in kayak modification (see his cockpit rim mods!) and he can create precision parts from fiberglass, carbon and epoxy.
After installing an electric bilge pump in his wife's Avocet LV he wanted to compare it to a foot bilge pump.
Not satisfied with the commercially available one he designed and fabricated his own one. The pump is a modified manual hand pump that was sourced at a marine chandlery.
The handle has been removed and a custom foot bracket made to optimize the action of the pump.
foot pump mounted in cockpit of a Nordkapp LV.
A reinforcing plate is mounted on the bulkhead. This version of a foot pump is mounted on the bulkhead instead of on a bracket off the foot pegs(http://www.hybridaustralia.com/).
Needless to say that a kayak must be just the right size for you with the forward bulkhead close enough to have this set up.
Extensive modelling has been done to achieve the right pedal size and leverage.
The strum box is enlarged to allow wider pick up and increase water flow.
details of the pedal: a custom one-off (no mold) unit made from fiberglass, carbon and epoxy.
strum box detail
The pump works extremely well and empties a flooded cockpit almost as fast as a Rule 500 electric bilge pump.
If your idea for a bilge pump does not include electricity, this foot pump seems to be probably the best solution.
Unfortunately Greg Schwarz is not interested in producing these units commercially (they would cost almost as much as a kayak, if he had to charge for his time making one).
If you really are confident with your fibreglassing and have the time and patience, this pump could be the inspiration for your version.
Let me know how your project turns out.