RV Water Heater Drain and Anode Replacement, Step by Step (Suburban and Atwood)

An RV water heater needs two things done once or twice a year: drain the tank and flush out sediment, and on a Suburban, check and replace the anode rod. Both happen through the same hole in the tank, behind the exterior water heater door.

The job takes about 30 to 60 minutes and needs a socket, PTFE tape, a rinse wand, and a new anode or plug. The step that matters most for the heater’s life is the one that takes no tools at all: making sure the electric element and the gas are off before you drain, and that the tank is completely full before you turn them back on.

Why Suburban has an anode and Atwood doesn’t

Suburban (SW6, SW10, SW12, and the Dometic-era Suburban models) uses a porcelain-lined steel tank. The lining always has tiny flaws, and any steel exposed to water would corrode. A magnesium or aluminum anode rod, screwed into the bottom of the tank, corrodes instead. It is a sacrificial part: it is supposed to dissolve, and when it is gone, the tank starts to go. A Suburban tank with a fresh anode can last decades; one that ran years with a spent anode rusts through.

• Magnesium is the standard and the most active. It protects best.
• Aluminum (or aluminum-zinc) anodes are used where magnesium reacts with sulfur-bearing water to make a rotten-egg smell. They protect a little less and last a little longer in some water.

Atwood (GC6AA, GC10A, G6A, and Dometic-branded Atwood designs) uses an aluminum-clad tank. Aluminum forms its own oxide layer and doesn’t need a sacrificial anode; installing a magnesium anode in an Atwood tank is wrong and the manual says not to. Atwood uses a nylon drain plug in the same position instead. You still drain and flush an Atwood; you just don’t have an anode to check.

Not sure which one you have? Look at the exterior door. A Suburban shows a large hex fitting at the lower left of the tank face. An Atwood shows a white or tan plastic plug. The data plate on the tank face says it outright.

Step 1Power off, both ways, and let it cool

1. Turn the electric water heater switch off at the inside panel. On most rigs it’s a rocker switch near the water heater or on the monitor panel.
2. Turn the 120 V breaker for the water heater off at the distribution panel. Do both: the rocker switch is easy to bump on, and some rigs wire the element to a switch at the heater itself.
3. Turn the gas water heater switch off. On older pilot models, turn the gas valve to OFF.
4. Let the tank cool. Water at the thermostat setting (typically 130 °F to 140 °F) scalds. Give it a few hours, or overnight.

The electric element must never run dry. Once the tank drains, if the element gets 120 V, it burns out within seconds to minutes, because it relies on water around it to carry the heat away. Element dry-fire is the single most common way people turn a 30-minute maintenance job into a parts order. Kill the breaker, not just the switch.

Step 2Shut off water and relieve pressure

1. Turn off the water pump and disconnect city water, or close the city water supply.
2. Open a hot faucet inside, preferably the one nearest the heater. Leave it open.
3. At the exterior door, lift the pressure relief valve lever (the brass valve with a lever at the top of the tank face). Water and air will spit out. Hold it open until it stops.

With the faucet open and the relief valve lifted, the tank is at zero pressure and air can come in as water goes out, so it drains fast instead of glugging.

Don’t remove the anode or plug with the tank under pressure. A 6 gal tank at 50 psi will shoot the plug out of your hand and the water at your face.

Step 3Remove the anode or drain plug

Suburban: put a 1-1/16 in socket on the anode hex at the lower left of the tank. Use a 6-point socket if you have one and a breaker bar, because anodes are often seized. Turn counterclockwise. Be ready: the remaining water comes out in a gush the moment the threads clear. Stand to the side.

If the anode won’t move, a short sharp hit on the breaker bar with a mallet works better than a long steady pull, and an impact wrench on low works well. Brace the tank face; don’t lever against the outer jacket.

Atwood: the nylon drain plug unscrews counterclockwise with a socket or wrench to fit (check the size before you strain; a damaged plug head is easy to strip). Don’t use an impact wrench on nylon.

Let it drain completely. A 6 gal tank empties in a minute or two, a 10 gal in a few.

Step 4Flush with a rinse wand

A water heater rinse wand is a short bent tube with a garden hose connection and a shut-off valve. Connect it to a hose, push the wand into the drain opening, and open the valve. Move the tip around the bottom of the tank and up the sides.

What comes out: white or tan flakes and grit (calcium and magnesium scale from hard water), gray sludge (spent anode material from a Suburban), and sometimes rust-colored water. Keep flushing until the water runs clear. A few minutes is usually enough; a heavily scaled tank may take longer.

Scale matters because it insulates the tank bottom from the burner, sits on the element, and takes up volume. A tank that heats slower than the numbers in the heat-up time guide often has a lot of scale in it.

Step 5Inspect the anode

A new Suburban magnesium anode is a smooth rod about 3/4 in across on a hex head. As it works, it gets thinner and pitted and caked with white deposit.

• Up to about half consumed: knock off the scale, reinstall it with fresh tape, check again next season.
• About 75 percent consumed, or the steel core wire showing anywhere along the rod: replace it. Suburban’s guidance is to replace when the rod is largely used; 75 percent is the common working rule.
• Barely touched after a year: unusual. The rod may not be making electrical contact (tape coating the threads can isolate it on some installations), or your water is very soft. Check that the hex bites into clean metal.

Typical life is one to two seasons for full-time or frequent use, and longer for occasional weekend use. Hard water, high water temperature, and full-time use all shorten it. An anode that is gone in a few months suggests very aggressive water, or electrical leakage to the plumbing, worth a check of the campground pedestal and your own grounding.

Suburban’s OEM magnesium anode is part 232767 on many SW models; verify against your heater’s model number, and match the length.

Step 6Reinstall with PTFE tape

Wrap three or four turns of PTFE (Teflon) tape clockwise on the anode or plug threads, looking at the threaded end. Start a thread or two back from the end so tape doesn’t get pushed into the tank.

Use tape, not pipe dope. The manufacturers call for tape, dope is messy to clean off the tank threads next time, and some sealants harden and make the anode harder to remove next year.

Thread it in by hand at first to avoid cross-threading. Then snug it up with the socket and add about a quarter turn. That’s all. The tape seals the threads; overtightening cracks a nylon Atwood plug and makes a Suburban anode miserable to remove next season. If it weeps after refilling, tighten a little more.

Atwood plug replacement: nylon plugs get brittle and threads wear. Replace the plug every few years, or whenever it looks cracked or the threads are chewed. Use a plug made for Atwood tanks; don’t substitute a metal plug, and never install a magnesium anode in an Atwood. Tape and snug it the same way.

Step 7Refill and burp the air out before power

1. Close the relief valve lever if you left it propped.
2. Leave the inside hot faucet open.
3. Turn on the pump or city water.
4. Let the tank fill. You’ll hear it, and the faucet will spit air and water. Keep it open until water runs steadily from the hot tap with no spitting for several seconds.
5. Close the faucet. Check the anode or plug for leaks.

Only now turn on the gas or the electric. On a 6 gal tank, refilling takes a couple of minutes on city water, longer on the pump. Don’t rush it. An element switched on to a partly full tank can still burn out if the top of the element is above the water line.

Step 8The relief valve weeps afterward

A day or two after draining, people often find the relief valve dripping when the heater runs. That’s usually not a bad valve.

RV water heaters are designed with an air pocket at the top of the tank. Water expands as it heats, and the air cushion absorbs the expansion. Draining and refilling the tank under pressure fills it completely with water, with no cushion. Heat it, the water expands, pressure rises to the valve’s rating (typically 150 psi / 210 °F), and the valve weeps.

To restore the air gap:

1. Turn off the heater and the water supply.
2. Open a hot faucet inside.
3. Lift the relief valve lever until water stops flowing. Air enters the top of the tank as water drains from the relief valve.
4. Close the lever and the faucet, and repressurize.

The air pocket slowly dissolves over weeks, so you may need to repeat this every few weeks. If the valve weeps constantly at cold pressure, or keeps weeping after you’ve restored the air gap, it may have debris on the seat or have failed; replace it with the same rating. Never cap, plug, or remove the relief valve. An accumulator tank on the pump also helps absorb expansion.

Winterizing timing and bypass positions

Drain and flush the water heater as part of winterizing, and inspect the anode at the same time. Some owners leave the anode out over winter so the tank dries and the anode doesn’t corrode in standing water; put a fresh one in when you de-winterize.

The bypass valves (one, two, or three behind the water heater, usually accessible from inside) route water around the heater so you don’t fill 6 or 10 gal with antifreeze. Positions:

• Normal (summer): water flows into and out of the heater. Bypass valve closed.
• Bypass (winter): inlet and outlet closed, bypass valve open. Water and antifreeze skip the tank.

The winterizing guide walks the valve positions in detail. In spring, set the bypass back to normal before filling. A heater switched on with the bypass still set leaves the tank empty and trips the ECO; see the won’t light guide.

Symptom → likely cause

Parts and tools mentioned

• 1-1/16 in 6-point socket and breaker bar (Suburban anode)
• Socket or wrench to fit the Atwood nylon drain plug
• Suburban magnesium anode (232767 on many SW models; verify) or aluminum anode
• Atwood nylon drain plug made for Atwood tanks
• Water heater rinse wand with garden hose shut-off
• PTFE (Teflon) thread tape
• Replacement pressure relief valve, 150 psi / 210 °F, if needed
• Bucket, gloves, flashlight

Questions people ask next

How often should I drain and flush the water heater? At least once a year, and as part of winterizing. Full-timers and anyone on hard water often do it twice a year.

Can I run a Suburban without an anode? Not for long. Without an anode the steel tank starts corroding through the lining’s flaws. If you remove it for winter storage, reinstall a good one before you fill the tank for the season.

Do I need to replace the anode if I only camp a few weekends a year? Check it every year. Light use stretches the life, but water sitting in the tank between trips still corrodes the anode. Replace it when it reaches about 75 percent consumed, regardless of the calendar.

Why is there no water coming out when I pull the plug? The tank may already be empty, the bypass may be set so the tank never filled, or a vacuum is holding the water in. Open a hot faucet and lift the relief valve lever to let air in.