Anyone have any recommendations on what type or brand of pump to use to get the grey water into the black tank?
I have a small Harbor Fright "utility pump", about $30 on sale, mounted vertically so its impeller is always submerged (VERY important, if the impeller runs dry it will wear out in seconds), and it moves gray water from a dedicated 3/4" outlet about an inch off the bottom of the gray tank (so it won't suck nasties into it that may be lurking on the bottom of the tank). It pumps the gray water to an inlet directly above the poo tank's main dump outlet, so if I get stalagmites or the Dreaded Mound Of Death blocking the dump valve it should help clear them. If that doesn't work, I can also jet higher-pressure city water in through the same inlet, obviously with check valves on the city water and gray water feeds to prevent cross-contamination.
My poo tank is about 25" high, so if I wait until it's full before dumping I should get a vigorous flow of caca through the slinky. I'm always amazed that the flat poo tanks in most RVs don't have more problems than they do with blockages and slow flow - they're just a poor design, but lack of space precludes anything better.
See, this forum has reverted yet again to discussing bodily waste. "It's not an obsession, we're just busnuts."