A surprising number of boats use the readily available sumps that can be found at your local marine store. I’ve found, though, that some of these units don’t hold up to the industrial use of living aboard, and others are prone to leaking around the lid when the boat is heeling. When retrofitting a gray-water system on an older boat, meanwhile, the off-the-shelf sumps often simply won’t fit in the small spaces available in the boat’s bilge.
I recently installed a custom collection tank on a boat, and designed it to resemble the one I built aboard our Reliance 44 ketch, Lyra, using PVC pipe pieces, common plumbing fittings and an electric pump. This easy-to-build system still works well after four years of living aboard. In that time, I’ve opened the tank itself on our boat exactly once (to check the float switch — it was fine). I’ve cleaned the pump diaphragm twice, each time removing items such as zip ties and paper clips. In the more recent installation, described below, I added a pre-filter to keep such items out of the pump altogether.