RV Toilet Repair & Replacement Guide (Thetford / Dometic)

RV Toilet Repair & Replacement Guide (Thetford / Dometic)

Most RV owners assume their toilet will work the same way it did on day one—that assumption is wrong. What actually happens is quieter and slower: a seal starts to weep, the foot pedal gets stiffer month by month, mineral deposits build up invisibly inside the flush valve, and by the time you notice anything serious, you’re usually three states away from a dealer and sitting in a campground full of people who can smell your problem as clearly as you can. The calls I field during holidays always follow the same script—panicked owner, kids nearby, some variation of “it’s making a weird sound” or “there’s water under the toilet.” When I ask how long it’s been happening, the answer is never “just started today.” It’s always been happening, but ignored. By the time someone’s dialing me up, what began as a five-dollar seal failure has usually metastasized into a full replacement conversation, complete with cleanup questions nobody wants to think about. This guide covers what I’ve learned pulling apart, repairing, and swapping out Thetford Aqua-Magic and Dometic 300/310 toilets—the two models that live in the vast majority of travel trailers and motorhomes—and I’ll take you through every fix from a quick seal replacement all the way to yanking the whole unit and installing something that’ll actually last, so you can get this sorted before the holiday weekend becomes a roadside emergency.

The Toilet That Actually Survives Year Two: When a Full Replacement Beats Another Seal Kit

If you’re past the point of chasing seal leaks and foot pedal stiffness on a factory Thetford or Dometic, you’re not fixing anymore—you’re replacing. A gravity-flush RV toilet swap is the one repair that actually improves your life instead of just buying you another six months of silence before the next drip.

Parts and Tools

• Replacement wax ring or rubber gasket matched to your toilet’s flange diameter (typically 3 or 4 inches for RV toilets)
• Stainless steel bolts and washers sized to fit your toilet’s base mounting holes, usually 1/4-inch or 5/16-inch
• New fill valve and flush valve seal kit specific to your toilet model (Thetford or Dometic)
• Replacement foot pedal assembly if the existing pedal is cracked, stuck, or stripped
• Soft-close seat and lid assembly matching your toilet’s bowl dimensions — check current price
• Silicone-based RV caulk rated for wet environments and compatible with your toilet material

Step-by-Step Instructions

Step 1: Shut off water and empty the tank

Turn off the freshwater supply valve at your RV’s main water inlet or the dedicated toilet shutoff if you have one. Flush the toilet completely to drain the bowl and tank. If water remains trapped, use a hand pump or turkey baster to remove it. This prevents spills when you disconnect the water line and protects your flooring from contamination.

Step 2: Photograph the existing setup and disconnect water

Take clear photos of how the water line connects to the fill valve inlet—note the fitting type and orientation. Use an adjustable wrench to loosen the compression fitting or push-to-connect coupling. Have a small bucket or towel ready to catch residual water. Keep the old water line; you may reuse it if it’s not kinked or damaged.

Step 3: Remove the old toilet from the floor flange

Locate the bolts securing the toilet base to the floor flange, usually hidden under plastic caps or trim rings. Remove these bolts with a wrench or socket set. Rock the toilet gently side to side to break the seal, then lift straight up and set it on a towel or tarp. Inspect the old wax ring or gasket on the flange; photograph it for reference if you’re unsure what type to buy.

Step 4: Clean and inspect the floor flange

Scrape away all old wax, gasket material, and debris from the flange using a putty knife or plastic scraper. Wipe the flange clean with a damp cloth and let it dry completely. Check that the flange bolts are present and not stripped; if they’re damaged, replace them now. Verify the flange is level and not cracked; a damaged flange will cause leaks even with a new toilet.

Step 5: Install the new gasket and position the toilet

Press a new wax ring or rubber gasket firmly onto the flange, centered over the opening. If using a rubber gasket, ensure the tapered side faces downward into the flange. Carefully lower the new toilet straight down onto the gasket, aligning the base bolt holes with the flange bolts. Do not rock or twist the toilet; pressing down unevenly can damage the gasket seal.

Step 6: Secure the toilet and reconnect water

Insert bolts through the base holes and thread them into the flange. Tighten in a cross pattern (opposite corners alternately) to ensure even pressure; do not over-tighten, which can crack the porcelain. Hand-tighten first, then snug with a wrench—aim for firm resistance, not maximum force. Reconnect the water line to the fill valve inlet using the same fitting type as before; hand-tighten, then snug with a wrench.

Step 7: Test flush and check for leaks

Turn the freshwater supply back on and listen for the fill valve to stop after the bowl fills. Flush the toilet several times and observe water flow and drainage. Check underneath the toilet and around the base for any water seeping from the flange seal or water line connection. Let the toilet sit for 30 minutes, then inspect again; a slow weep may take time to appear. Caulk around the base with RV-rated silicone once you confirm no leaks.

What works

• Foot pedal doesn’t require you to muscle it after three months—it glides, and it stays gliding because there’s no complex flush valve to jam up with mineral deposits.
• Soft-close seat eliminates the midnight bang that wakes your campground neighbors and reminds you how thin RV walls actually are.
• Comfort height means you’re not doing a squat every time you sit down—serious quality-of-life gain when you’re living in 200 square feet.

What doesn’t

• Installation isn’t a 20-minute job if your floor is warped or your flange bolts are corroded—you’re looking at cutting out old caulk, potentially re-shiming the base, and maybe drilling new holes.
• Amazon ships these with minimal padding; I’ve unpacked units with the soft-close hinge already cracked from the carrier dropping the box.

I second-guessed the SEAFLO brand the first time because it wasn’t the OEM name I recognized, but two flippers and a full-timer later, I realized that’s actually why it works—it’s not carrying the design flaws the originals shipped with. Grab the SEAFLO RV Toilet, Comfort Height 18.4″, Gravity Flush Foot Pedal, Soft Close Seat, Camper Toilet for RV Motorhome Travel Trailer, White, SFRTPH-01-01, 4-Year Warranty and plan a full afternoon for installation.