RV plumbing is a small house system built to move. Water comes in one of two ways, gets heated in one place, is used at a handful of fixtures, and leaves into one of two tanks. That is the whole thing. What confuses new owners is the vocabulary and the valves. This guide walks through the water in the order it flows.
Water in: two sources
The fresh water tank. A plastic tank under the floor or in a compartment, filled through a gravity fill or a locking inlet. A 12 V pump draws from it and pressurizes the lines. On a Black Series HQ the 12 V water pump ($99.00) is the standard unit, and tanks range from a 10 gal auxiliary to the OEM tanks and a 16 gal stainless drinking tank.
City water. A threaded inlet on the outside wall that takes a garden hose from the campground spigot. The campground's pressure runs the system directly; the pump stays off. The inlet contains a check valve so pump pressure does not flow back out. The RV city water inlet with brass check valve ($12.99) is a standard replacement; the Fiamma lockable inlet ($39.99) is the common upgrade for the gravity fill.
Two rules: always use a pressure regulator on city water (campground pressure can exceed what RV fittings tolerate), and always use a drinking-water-rated hose, never a garden hose.
Filtering
Campground water varies. An inline filter on the hose catches sediment and chlorine; an under-sink or countertop unit polishes drinking water. Start with the 6-layer 0.5 micron filter with stand ($139.99) or the reusable brass sediment filter ($69.00). Replace cartridges on schedule; a clogged filter is the number one cause of low pressure and of tankless heaters that will not light. See the water filter replacement guide.
The pump and the pressure switch
The pump runs when pressure drops (you open a tap) and stops when it climbs back (you close it). A pump that runs with all taps closed means a leak somewhere; a pump that pulses while a tap is open means low flow. Both are covered in the water pump cycling guide. Keep the strainer at the pump inlet clean.
Hot water
RVs use one of three heaters:
- Tank water heater (6 or 10 gal, propane and/or electric). Slow to heat, holds a reserve. Has an anode rod that needs annual replacement on steel tanks; the anode rod and flush kit ($34.00) covers it.
- Tankless (propane, 12 V ignition). Endless hot water, no reserve, needs minimum flow to ignite. Standard on Black Series HQ; the tankless water heater ($380.00) is the OEM unit and the 12 V tankless guide explains use and care.
- Electric-only on some small campers; shore power only.
Every heater has a bypass valve so you can winterize without filling the heater with antifreeze. The water heater bypass valve ($43.00) and the bypass valve winterization guide cover it.
Fixtures
Kitchen faucet, bathroom faucet, shower, outside shower, sometimes an outdoor kitchen. RV fixtures use lighter fittings than household ones (commonly 1/2 in NPS swivel nuts) and a water-saving shower handset with a shut-off is standard. The faucet replacement guide covers the connection types.
Water out: gray and black
Gray water is everything from sinks and the shower. Black water is the toilet. They go to separate tanks, each with its own gate valve at the outlet, both draining through one sewer connection. Some campers, including many off-road models, combine the two or use a cassette toilet instead of a black tank. The 26 gal gray/black tank ($380.00) is the Black Series OEM unit.
Rules that prevent most problems:
- Keep the black valve closed at a full-hookup site until the tank is at least two-thirds full, then dump. Leaving it open lets liquid drain and solids pile.
- Dump black first, then gray, so the gray water rinses the hose.
- Use a tank treatment in the black tank; the 32 oz digester ($33.00) is enough for a season of weekends.
- Rinse the black tank with a tank cleaner wand ($45.00) a few times a season.
The gray/black tank replacement guide covers the tanks themselves; the sanitary waste valve guide covers the valves.
Vents and traps
Every drain has a trap so tank gas cannot come back into the cabin. A household P-trap relies on standing water, which sloshes out on rough roads. A HepvO waterless trap ($34.99) uses a membrane instead and is the standard fix for a camper that smells of gray tank after a drive. Tanks also need a vent to the roof; a blocked vent causes slow drains and gurgling.
Level gauges
Tank level sensors are notoriously wrong, usually because tissue or scale sticks to the probes. A 5-bolt flange sender ($19.99) replaces a failed one, and a digital LED level gauge ($34.00) is a worthwhile upgrade on the fresh tank. See the level gauge guide.
Freezing
Water expands when it freezes and splits fittings, pump housings, and faucet cartridges. If the camper will see temperatures below freezing while unused, winterize it: drain, bypass the heater, blow out with a blowout adapter ($12.00), and pump antifreeze through. If you camp in freezing weather, insulate lines with pipe foam, add tank heater pads, and use a heated water hose at the spigot. The whole Winterization collection is organized around this, and the Winterization Service ($183.20) does it for you.
The five-minute pre-trip check
Fill the fresh tank, turn on the pump, listen for it to build pressure and stop. Open each tap until the sputtering stops. Check under every sink. Confirm both waste valves are closed. Look at the city water inlet cap. That is it.
Shop this
- Water Pump 12V — $99.00
- RV City Water Inlet with Brass Check Valve — $12.99
- HepvO Waterless Sink Trap — $34.99
- Water Heater Bypass Valve — $43.00
- Water (collection)
- Winterization (collection)