So, you’re wondering how an RV’s plumbing system works, huh? It’s a great question – and you might be surprised to learn how similar they are to your home’s plumbing! You might also be surprised to learn where they differ dramatically! In this article we’ll walk you through a typical RV’s plumbing system and by the end you’ll be able to quickly and easily identify the differences between an RV and home plumbing systems!

Household Plumbing

P trap and water supplies in home plumbing
P trap and water supplies in home plumbing

Household plumbing systems typically drain either directly into a city sewer system or into a septic system. The sinks, showers, and toilets have P-traps and are vented to the roof of the house to keep sewer gasses from entering the house.

Dishwashers and washing machines usually use either air gaps or Studor vents to prevent sewer gasses from entering the house. 

The water supply to a home is either from a city freshwater supply or from a well. 

RV Plumbing 

Gray water holding tank mounted under an RV
Gray water holding tank mounted under an RV

RV plumbing systems drain into either a gray water holding tank – if it is water from the sinks, showers, dishwasher and washing machines – or into a black water holding tank if it is from toilets.

RV kitchen sink plumbing over water heater with water supply lines
RV kitchen sink plumbing

The sinks in an RV use P-traps to keep sewer gasses from entering the RV. 

RV kitchen plumbing Studor valve and cold water supply line
RV kitchen plumbing Studor valve

The showers can use either a P-trap or a HepVo valve to keep sewer gasses at bay. Dishwashers and washing machines often use air gaps such as Studor vents to stop sewer gasses.

RV waste water vent and cap
RV waste water vent and cap

RV toilets use a vertical vent, similar to the vent stacks found in household plumbing, that is usually vented at the roof of the RV. 

Keeping the black water holding tank valve closed, unless dumping the tank, is essential. 

Full Hookup Camping

If staying at a campground with full hookups, you can leave the gray water holding tank valve open.

P trap added to an RV sewer discharge hose on sewer hose support
P trap added to an RV sewer discharge hose

It is a good idea to add a P-trap in the discharge drain hose with some water in the P-trap as an extra line of defense against sewer gasses.

Heated water supply at RV campsite at a full hookup campground
Heated water supply at RV campsite

Fresh water is supplied by either the campground from a garden hose style spigot that is then connected to RV by a garden hose, or from a fresh water holding tank and an electric water pump. 

The Takeaway

Since RV plumbing systems are patterned after household plumbing systems it is easy to see the similarities between them. RV plumbing is just slightly more complex due the mobility of the RV. 

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