RV holding tanks are one of the most discussed RV related topics online and around campgrounds. There seems to be a fair amount of mystery surrounding them as well. Fortunately, they are relatively simple devices. We will cover all of the components in and around the three types of holding tanks that are typically on an RV. The most common RV holding tanks are freshwater, gray water and blackwater. 

Freshwater Holding Tank

Used to store freshwater that will  supply the RV with freshwater for  the sinks, showers, water heater, and toilet flushing mechanism.

  • 20-100 gallon capacity
  • Usually has 4 ports for connecting inlets and outlets to and from the tank
RV roof vent and camp
Roof vent and cap
  • Vented 
  • Frequently has 4 sensors (Full, 2/3rds, 1/3rd and a grounded sensor)
RV fresh water low point drain out
Fresh water low point drain out
  • Generally has a small drain at the low point of the tank
RV water pump
RV water pump
  • Distributes the water throughout the RV using an electric water pump

Gray Water Holding Tank

Used to collect and store water from the RV’s drains including sinks, showers and sometimes dishwashers and washing machines.

  • 8-100 gallon capacity
  • Usually has one inlet from the RV sinks’ and showers’ plumbing
RV gray water discharge port
Gray water discharge port
  • One drain outlet for dumping the tank
RV vent hole cut in to gray water holding tank
Vent hole cut in to gray water holding tank
  • Vented into the waste vent stack
Sensors on an RV gray water holding tank
Sensors on gray water holding tank
  • Frequently has 4 sensors (Full, 2/3rds, 1/3rd and a grounded sensor)

Blackwater Holding Tank

Used to collect and store human waste and toilet paper from the RV toilets. 

  • 15-100 gallon capacity
Pipe running from an RV toilet into the black water holding tank
Pipe running from toilet into the black water holding tank
  • Usually has one inlet from the toilet
RV black water holding tank discharge port
Black water holding tank discharge port
  • One drain outlet for dumping the tank
RV roof vent for the black water holding tank with cap on
Roof vent for the black water holding tank
  • Vented into the waste vent stack
RV sensors on a black water holding tank
Sensors on a black water holding tank
  • Frequently has 4 sensors (Full, 2/3rds, 1/3rd and a grounded sensor)
Ledge used for mounting a black water holding tank to the frame rails of the RV that can often collect waste and paper
Ledge used for mounting a black water holding tank to the frame rails of the RV that can often collect waste and paper
  • Sometimes it has ledges to keep it in place in the RV frame rails. These ledges can collect waste and toilet paper

The Takeaway

While RV holding tanks may seem somewhat mysterious, they are relatively simple devices that, when used and maintained correctly, can be easy to take care of. They add many of the conveniences of a house while on the road. RV holding tanks share similarities with each other and that also helps to demystify them overall.

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