Fresh Water Tank Upgrade

The perfect tank turned out to be 40 gallons. I went from a 12x12x38 to 14x18x42, enlarging the space under the bed somewhat by cutting away some extra overhang from the kitchen wall (about 2 inches). The manufacturer used exclusively square-drive screws for all the RV carpentry, and I was lucky to have the right screwdriver tip to be able to remove these just prior to them stripping completely (they aren't high quality screws I'm afraid).





Fitting it in was a simple matter of measuring and creative sawzall work, but making the rest of the connections was not so trivial.

First of all, I moved the water level sensors to the new tank (drilling 3/8" holes in what I can only assume were the right places). These were hard to remove, even harder to insert, and they leaked. Some silicone sealant under and on the stud threads helped.



Then it took me a little while to notice that the drain and the vent aren't the same size - drain is 3/8" tubing while vent is 1/2". (Not only did I get the angle adapters switched, but I was using the wrong size hose clamps). Hose clamps were their own saga, as the ones I carefully removed are stepless crimp clamps, and they aren't really reusable. I wound up having some success with fuel injection hose clamps in their place, with some (very wet) trial and error.




I also had to relocate the pump a little, and to make this easier I wanted the pump outlet hose to be longer (it's a reinforced braided hose). I bought some reinforced 1/2 hose, only to realize that it won't work - the RV hose is special - a rigid reinforced outer layer on a very soft inner rubbery layer (I believe it's exactly this one - an RV specific hose).



I couldn't find anyone locally who stocks this in the right size, so I gave up and made my own semi-reinforced hose by slipping 5/8 ID tubing over 1/2 ID tubing. I might replace this in the future, but it's holding OK so far with my 55 psi faucet pressure.

Finally, the filler hose is attached with some caulk and a hose clamp. I don't understand why such a rigid hose is used when it isn't a good fit over the the tank's filler fitting - it's so loose that you need wrenches to tighten the hose clamp. Even then, it doesn't make a good seal unless you use quality caulk (eg GE Silicone II) very generously and let it dry for a while.



In the end, with all these problems resolved, I have a 40G fresh tank, yet my grey and black are still only 28G each. The black obviously doesn't need to be so large, so I researched some rather complex methods for transferring the extra grey water into the mostly empty black tank. Ultimately I came across the simplest method of all - just leave the cap on, and open both valves to equalize the tank - the tank with higher level wins (you then close the valves). This is a messy solution because at the dump station you will be greeted with a quart of not-so-exciting content trapped behind the cap. A more classy variant is to use a 3" Twist-On Waste Valve (as Amazon calls it) - instead of the cap.

This solution works just fine, and cross-contamination between black and grey is probably not so much of an issue. What turned out to be an issue was smell (when flushing after equalizing) ... apparently while my black tank never had much of an odor issue thanks to Odorlos enzymes, my grey tank did not receive as much care in this respect. Who knew? The P-traps on all the sinks kept me from knowing that there is an issue. So in short, if you plan to equalize your tanks to extend your stay, make sure your grey tank doesn't smell.

All in all I'm quite satisfied with the upgrade, the 40G gives the two of us about 2 days of care-free usage, and probably twice that with super-saver usage. Though I'm told that it's still not enough to properly wash long hair.