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Your RV provides running hot and cold water and drainage systems for your convenience. The system is self-contained, and while similar to the plumbing in your home, there are differences.
The first part of the system is a tank of fresh, clean potable (drinkable) water stored in an onboard tank. Tank sizes vary, but are typically 20 to 40 gallons in size. While it would seem convenient to have much more fresh water on hand, there are very good reasons to limit the size of the fresh water tank. Water is HEAVY, impacting the handling and efficiency of your RV and reducing the carrying capacity available for other cargo. Water is readily available and quite inexpensive too, so it usually makes more sense to get what you need when you need it, instead of carrying a heavy load everywhere. Also, fresh water has to ‘go somewhere’ after you’ve used it, so the amount of fresh water you carry also impacts the size and weight of the waste tanks you need.
You’ll find a water fill inlet somewhere on the outside of your RV. Use a hose designed for potable water and a source of high-quality drinking water to fill the tank. Take care that no foreign material enters the fresh water tank, and keep the water fill inlet closed whenever possible
The fresh water tank is connected to a water heater. Two types of water heaters are in use in RVs: Tank-style water heaters are similar to standard residential gas water heaters, using a gas flame to keep a quantity of water at a pre-determined temperature. The gas burns when needed to heat the water in the tank. This type of water heater limits the amount of hot water available to users by the capacity of the hot water tank - typically 6 to 10 gallons. Tankless water heaters heat water as the water passes through a heat exchanger that is heated by a gas flame. Tankless water heaters are instantly heating water as it is used, and are designed to maintain the pre-set temperature regardless of how much water is sent through the exchanger. (Learn more about Tankless water heaters here)
Once water in the fresh water tank is filtered by the Pre-Pump filter, pumped through tubing by the 12V pump, with one line passing through the water heater, the water is directed to the various faucets.
As an alternative to the onboard water system pressure pump, many campgrounds and other recreational facilities provide pressurized connections to drinking water for RV campsites. You can connect your RV to the supply of fresh water using a hose designed for potable water, and use the campground supply instead of the water in your fresh water tank.
Typical RV systems have two waste tanks: A ‘black tank’ for sewage from toilets, and a ‘grey tank’ for the drains in sinks, showers, and tubs. Both of the waste tanks are of limited capacity, typically 20 to 40 gallons each. Most RVs are equipped with gauges that use floats to monitor the fluid levels in the tanks.
Unlike the fresh water side of RV plumbing, the sink, shower, and tub drains use gravity instead of a pump to move water to the grey tank.
The fresh water system provides water to toilets. The toilets then use a sealed, self-contained pressurized system to evacuate waste and reduce odors. The vacuum pressure sends these black water wastes to the black tank. Seals need to be working properly for the system to perform well. The nature of the system also makes it important to keep anything that may clog pipes or drains out of the toilet. This includes the requirement that toilet paper formulated for use in RV toilets be used in place of ordinary TP.
RV plumbing is somewhat similar to residential plumbing but the differences are important to note:
Grey and black tanks should be emptied when they near capacity. In some RVs a single drain line connects the grey and black tanks so they can be emptied at the same time; in other installations, two drains are used and tanks are emptied separately. All RV waste must be dumped in compliance with local regulations. Check to make sure you know and follow these regulations. Provisions for dumping RV waste are available at most public and private campgrounds, many RV dealerships, and certain rest areas and travel facilities.
Typically the dumping process involves connecting one end of a lightweight, collapsible, large-diameter tube to the RV drain line, and the other end of the tube to the sewer opening. Tubing designed for this purpose are readily available from any RV supplier. The tube used to drain sewage should be free of kinks, and provide a down-stream path for the flow from the tank to the sewer. With the hose in proper position, it is safe to open the valves on the RV drain line so fluids can drain from the tank. Some RVs include a special port that allows a hose to be connected so fresh water can be used to flush out the waste tank to complete the process.
Because of the way it is used, the sewage hose should be dedicated solely to the task for which it was designed. Disposable gloves are also useful.
For all the details of the Dump Station/tank draining process, see our article on Dump Station Basics.