Today I’d like to talk about my design for the holding tanks, and how my RV will be custom designed in this aspect. The image above (larger version) gives the approximate layout of how I’m planning on handling the fresh, grey, and black tanks.
The tanks are going to be technically inside the trailer, not mounted underneath. This is going to be accomplished by placing the tanks on the original floor provided by the manufacturer then building an additional floor on top of the tanks.
I’m using the wheel well height as my guideline. My understanding, at this point in time, is that the wheel wells will have a height of 10″ inside the trailer. If I were to place my new floor on top of this, it would give me 10″ of room to work with in which to place tanks.
Because these tanks are designed to hold many hundreds of pounds of water, and do so in a moving vehicle, I’m assuming they’re pretty stable and can probably withstand a bit of weight on top of each one of them as well. Of course the tanks themselves are not designed to be the primary structural support for the additional floor layer, but they will likely play a role.
For the additional floor I’m going to be adding 10″ sections of 2×4’s throughout the layout. With enough of them, I can provide probably a couple dozen mount points from which the weight of the additional floor can be distributed.
With the addition of the semi-floating floor above these tanks, it leads to having cavities in the space between the floors, and I’m going to be taking advantage of that space as well. I’m planning on multiple “trap doors” in the kitchen/bathroom areas that will let me access this void. Between the shower and toilet will be a trap door that will give me the primary access to most of the plumbing lines. In that area will be a couple of water pumps and likely a bunch of other plumbing-related accessories.
Under the dining table and in the kitchen cabinet will be additional trap doors that will give me access to the spaces near the grey tank that I can use for carrying illegal substances… I mean storage!
What I’m most pleased about with this void is the extra nearly 38 cubic feet of storage that is added in the rear of the unit that will be accessible from the utility area. This will be fantastic for storing any larger or longer items such as folding chairs, outside tables, outdoor rugs, or anything of that nature.
For people familiar with RV systems, there’s probably two questions or thoughts going on now: “My, those are some big tanks!” and “Why two water pumps?”
For the first thought, yes, those are large tanks. For an RV of this size, the tanks are somewhere between 2 and 5 times what might be commonly found from RV manufacturers. My goals with large tanks was to be able to comfortably boondock for at least 14 days at a time, and I really like to take a daily shower, so that necessitates a sufficient volume of water.
As for the dual water pumps, I’m borrowing a trick from “green” houses. When flushing the toilet, one does not really need potable water. Since it’s not meant for consumption and instead is meant only as a vapor barrier and a transfer mechanism, grey water will suffice. This has a couple nice advantages for an RV:
- By not using water from the fresh tank, the fresh water lasts longer.
- By taking water from the grey tank, the grey tank is effectively ‘larger’ because it’s partially emptied each time the toilet is used.
I may change the tank sizes a bit, but there’s something comforting in having nearly equal-sized fresh, grey, and black tanks. Technically, I should probably increase the ratio of the fresh tank to the other two, but I don’t have to tackle that issue for a while yet.
Some of the other lines in the diagram indicate the fresh-water fill line and the vent lines. For the fresh water intake, I’m using a gravity-fill intake (exclusively) which is accessed from the rear utility area. This saves me from needing water pressure regulators and an additionally complicated bypass system for the water pump. (And since I’m planning on spending most of my time away from utilities anyways, it works out fine.)
The orange lines are vent lines. Technically the fresh tank’s vent line is more of an overfill tube, but it’s mechanically similar. The fresh water’s vent line will come out right next to the gravity input port, so it’s really obvious when the tank is full – it starts spitting water back out at you. The other “real” vent is a shared vent between the black and grey tanks. I’ll make sure to run the lines up above the secondary floor before joining them to prevent any cross-contamination of fluids, but otherwise it’ll work out fine.
The placement of the drain lines is very approximate at this point. That’s one place where I will actually have to cut giant (3″) holes in the original floor in order to route the PVC pipes to the outside. If I can, I’ll try to make those holes somewhere I can access them via one of the trap doors. There’s a lot of stuff I’m cramming into that main plumbing area trap door, so I may re-imagine and redesign that before construction actually begins.