This was one of the least complicated systems, a basic RV plumbing system, with increased capacities.  The are only two fixtures, the bath tub and the toilet.


The original goal was to have a minimum100 gallon fresh water capacity.  Pending experience, this should last for two days, considering the conservation gained with recirculated wash.

As it turned out, the capacity is about 120 gallons.  Fresh water will be held in a reservoir made of PVC cylinders.  These are basic 10" diameter pipes in a vertical orientation.  This allowed fabrication without special equipment and eliminated "sloshing" in the tank.

Here is a spreadsheet for use calculating tank size and capacity for either a cylindrical or rectangular tank.

Holding Tanks

Gray water from bathing will be stored separate from toilet black water.  Gray water holding capacity should be at least half the fresh water capacity.  Custom built tanks are planned to maximize capacity and optimize weight distribution.  It will be acceptable to dump gray water more frequently than filling fresh water.  Capacity of the black water holding tank will depend on its final location and truck/body details.  Depending on final tank design, a macerator pump may be used to evacuate the gray water tank.


The water heater should have quick recovery and require little maintenance.  A ten gallon Atwood unit with both LP Gas and 110 volt electrical heating was chosen.  Atwood also offers an option to tie the heater into the vehicle's cooling system to capture additional heat from the engine.  This option was not chosen primarily because of the distance between the engine, in the front, and the water heater, at the very rear of the vehicle.  LP Gas will be the primary heat source.  The electric element will only be used while the generator is running and only one of the two high power electrical appliances, Air Conditioner and dryer, is running.  A lockout mechanism will be required to prevent all three systems from being turned on simultaneously.

Water Supply

The vehicle will have an integrated, self-retracting hose system for filling the fresh water tanks.  The hose reel system was custom built by Hannay Reels, a leader in industrial reels, to Paws At Your Door specifications.  The spring loaded system supplies and retracts up to 100 feet of 1/2" industrial hose.  Filters and pressure regulator will be integrated in the system for protection.


The version 1 vehicle used the largest available RV pump, the ShruFlo 5.7 SmartSensor.  Barb found this barely adequate.  Adding a small accumulator tank, the ShruFlo 24 oz. model, merely demonstrated the effect of an accumulator tank, but didn't have enough capacity to be practical.  An accumulator tank is intended to be a "cushion" for the water pump.  It reduces the number of times the pump switches on and off, thereby extending the pump's life.  From the faucet's perspective, there is a strong, steady flow of water, for a brief period, after starting the flow, until the reservoir is depleted and the flow is just the output of the pump.  Since the accumulator is essentially a balloon system that stores about half its rated volume in water and keeps it under pressure, the 24 oz. unit was inadequate.

We ended up selecting a FloTec pump designed to power a small house.  These are typically used for homes withtheir own wells.  the 1/2 horse power pump is rated at 8 gallons/minute at 40 PSI, and incorporates a 15 gallon accumulator tank.  This offered plenty of capacity.  The cost of this performance is size and power consumption.  The pump runs on either 230 or 115 VAC, whereas the RV-style pumps run on 12 VDC, and the accumulator tank was much larger.  We have AC power available, the pump will be powered from the inverter, with a maximum draw of 9.4 amps, and we found space for the pump/tank assembly.

Up Water Heater