New 5'vr has a galley grey water tank and grey tank for the shower(?) along with a black tank. Old unit just had one grey tank. Going to a cg with full hookup for first time this summer. Dumped in sequence (black then grey) before but can I leave one grey water valve open or should I leave both closed until ready to dump black tank with the new unit?
Also, pulled many miles with GN stock trailers and always blocked jacks / landing gear. Do the same with a RV?
I keep both of my grey tanks closed until I need to dump them, even when hooked up to sewer. Too many stories of sewer flies, and maybe other critters, getting into the tanks for me to want to leave them open.
I always dump tanks in the order of their cleanliness. Black first followed by the galley followed by the gray water. With lots of food deposits and grease from cooking in the galley it is often nearly as rank as the black tank.
Also might consider, the REASON for keeping dump valves closed is to accumulate enough liquids to flush out solids and there can be a fair amount of solids in a galley tank.
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Our shower also fills up much quicker than the galley so I will dump it when it is needed but I am cautious to make sure it is full when it's time to dump the black tank. Then I dump black, galley and shower, this way I have the cleanest water last with some soap going through the hose before storage.
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If you have, or add a tank flush system, especially for the black tank, you really won't have the issue of what tank is full or empty with the time to dump the black tank. I prefer to always travel with the gray tank empty, unless I am traveling from a location without sewer connections.
I put a low spot in the slinkey to add another trap - that way everything flows out, and sewer gasses / flying critters can't get in. I have the twist on valve mentioned, if I was worried about critters, I can leave the shower tank open, and just crack the twist valve open so it drains very slowly. If it takes a day to fill the shower tank, the valve has to be open enough to drain it in a day. I can;t think of much that can climb a 3" sewer line, walk across the empty slinky, swim through the trap in the slinkey, climb to the twist valve, then squeeze through the 1/16-1/8" it is open.
The full hookup is just a convenient dump station. When I setup, half of the time I don't even get the slinky out. If we only stay about 3 days, I get the thing out when we go to leave. Otherwise, I go dump the grey and galley about every three days. Nice thing about this system is when I finally dump the black, I have a lot of cleaner stuff on hand to wash out the slinky.
I like the idea of a twist on valve. That way, I can keep both black and grey valves closed, then when the black tank is near capacity, empty it, close the twist on valve, open the grey valve and let it run into the black tank, then open the twist on and drain everything. That way, the black tank gets a "free" rinsing, similar to what I do with the macerator pump.