I can't claim credit for this, I found it here at duckworks (thanks By Tim Ingersoll - Superior, Wisconsin - USA) but I thought it would look a lot better on my boat than a grey / black plastic thingy.
I cobbled one together out of scrap plywood to see if it simply functioned. I didn't want to spend a lot of time and effort and expensive wood to find out that it trickled water out, or had to be made to perfect tolerances.
It was easy to make, it moves LOTS of water with very little effort. It does splash water out the top where the handle comes out, so I need to try to make a "seal" there with rubber.
I need to try it with a pipe out the bottom to see how well it primes, but I think I will be putting my whale gusher urchin up on ebay shortly.
If it will self prime well enough, I see one each side of the boat, with a pipe to the other side, so that I can pump out the boat while I'm on the windward side.
Photos and test results for self priming to follow. But I've a Math project to hand up, so it may be a little while.