We needed a way to hose off the dogs and people after they come aboard from the beach. I bought an RV pump because I didn't want to mount the pump below the waterline as is required by the typical centrifugal washdown pumps. The RV pump is self priming and has a pressure shut off, but should have a strainer to keep the valves from clogging.
After I bought a tiny strainer (<$10), I decided I'd like something larger so I didn't have to clean it so often. I was inspired by a plastic SOS pad that I had lying around.
I measured the pad and found it would fit pretty nicely in a 3" PVC pipe. I had a time figuring how to make the 'filter' housing out of PVC, be able to seal it AND get it apart to clean it. After poking around in the Home Depot plumbing section I found the answer - a hose clamped rubber pipe cap. This was just the ticket - the caps were thick enough to take a threaded fitting and still stay water tight, but to be on the safe side, I cut a PVC coupler in half and used it squeeze the rubber from both sides.
The thru hull takes a 1" hose and the pump takes a 3/8" hose. I like the idea of a 1" supply because it can drain the filter when the boat is back on the trailer, hopefully eliminating the need to clean it. So I put a 1" fitting on the 'in' side and a 3/8" fitting on the 'out' side.
Rather than use the SOS disc that inspired me, I opted for a new Scotchbrite pad which I could cut just a little larger for a good snug fit. I would have been comfortable just leaving it at that, but I had some stainless screen from another project so I cut a couple circles to sandwich the pad.
And there you have it. A nice big filter to keep trash out of my pump.
A piece of clear pipe of some kind would have been nice so I could see what was going on inside, but I already had $15 in the project and didn't feel like it was necessary, at least for now.
I'll mount the filter vertically, well above the waterline, with a straight run to the thru hull for optimum self cleaning/draining.