tinstartrvlr wrote:
Didn't find any loose connections or holes in the hoses. Freezing hasn't been an issue since I fulltime and have had no problem keeping things warm (I leave cabinet doors open as well so heat can get to the plumbing).
I didn't realize they can just fail. FWIW, I do recall some whistling noise from the valve in the past when the flush was running; just assumed it was normal. Maybe it was a sign of impending failure?
Either way I'll start by replacing it and see if that fixes it.
Thanks all for the help.
The make Plastic and Brass(metal) valves. I would use the metal check valve. Doug
https://www.google.com/search?q=black+tank+check+valves&tbm=isch&tbo=u&source=univ&sa=X&ved=0ahUKEwi-zMCPqOTVAhVIJCYKHYTlDFkQ7AkIowI&biw=1024&bih=571#imgrc=io5ltrlK4Bm3aM:&spf=1503180643499