Yesterday I put water in the camper and a little bleach to clean out the systerm. Alas, our Shurflo 4009-101-A32 pump made the usual sound but pumped nothing. I have to admit I neglected to blow out the system before we had temperatures in the low-mid 20s.
I removed the pump and took it all apart and all looked ok. Admittedly it's hard to tell. After consulting Four Wheel Camper, they
sent a video which mentioned
the check valve sometimes gets jammed. Sure enough, ours was jammed pretty badly, perhaps due to ice. Now it's working fine, pumping water out of a bucket at a great rate. So I'm mentioning this in case someone else has an issue.
Note that the 4009 model is 20 psi. I couldn't find a pump at such a low pressure in some searching, but FWC has one they would sell to me. Other pumps were in the 50 psi range, which may instigate more leaks in obscure places hidden in the camper -- who knows. We always use a pressure reducer if using shore water.
There's a black plastic manifold in the same compartment, where shore water, pump water, and sink are all connected. Alas, this part leaks from one of the end caps. Replacing the O-ring didn't fix it. Maybe there's a small crack due to ice? Anyway a new part is winging its way from FWC for about $30. It's one of those parts where I didn't even know what it's called... and glad to have them send the right one with all the right diameters.