This was in a Winebago and the black tank was in the center rear of the coach and high up mtd to the floor behind the gen on one side and storage on the other. My dump valve was on the end of six foot of multi 90 degree bends of abs drain pipe. Worked just fine and the pipe gave me an extra few gallons of capacity. I was headed back to McKeesport, Pa. in Oct. and I wanted to freezproof my holding tanks. I left the long run of abs exposed and installed a multi coil of flex tubing in the in 2 inches of polyisocynite foam that covered the bottom of the tanks and also wrapped it around all my pipes for gray water. I had imbeded remote thermometers on both tanks to monitor their actual temps and also imbeded the bulb from a freez switch from a heatpump. The freeze switch was set for 35 degrees and when it contacted it turned on my house water pump and opened a water valve from a washing machine that put hot water from the propane fired hot water tank to the heating coils. I switched it on in the winter and left it on and whether I was home or asleep or gone it automatiocally kept all my lines and tanks from freezing. My fresh tank was in the coach and also protected caus the hot water drained back into the fresh tank and that water ran hot for awhile before the system caught up with itself and shut off. All I needed was propane that would last a couple weeks on a fill and battery that would go a month with that trickle intermittant drain for pump power. I installed a rod to the gray tank as that was a straight shot under the coach.
In my bus I expect to use the hot water to heat my fresh tank in the same way and to build my black and gray over my fresh so the heat from the fresh will raise their temps. I will be able to adjust the temp of the fresh to achieve this. Holding the temp of 100 gallons of water at 35 degrees in a well insulated tank should cost
? I don't want to heat the entire wet bay and worry about door seals as well and have the tank heated through convection although many are having success with that methode.
My 2 cents worth.