ShurFlo
I installed a ShurFlo Blaster ($85 from West Marine) in my C-30. It seems to have adequate power for washing off the anchor and general wash down. West Marine carries other, more powerful and more expensive pumps to $240. The most critical aspect of installation is wiring, it's best to stay as close as possible to the batteries and to use an adequately large gauge wire. The current draw is significant which is one of the reasons I didn't buy a more powerful model. It's best to use a separate circuit breaker. You need to use a reinforced hose similar to that used in your pressure water system (min 40 lb burst strength). Be wary of sharp bends which can collapse the hose (I had to use ells in two places. You also need to install a suitable filter on the inlet line. If you mount the pump in your anchor locker you can hook your hose directly to the pump and skip the deck fitting. Installing a deck fitting is pretty straightforward. I'm not an expert, but I don't think there is any way you could pump wastewater into the washdown pump, especially if you keep the flipper valve closed on the head.
