How to Replace Thetford Style II Toilet Ball Valve Seal Without Removal

Bottom Line Up Front

WARNING: Turn off water supply and disconnect water supply before beginning any work. Unfortunately, you cannot replace the ball seal in your Thetford Style II toilet without removing the toilet from the floor and partially disassembling it. The ball seal is located inside the toilet mechanism where the waste valve ball sits, requiring access from underneath. However, before you commit to this repair, there's about a 30% chance your water retention issue is actually caused by a simpler problem - a warped or debris-covered ball valve that just needs cleaning and adjustment, which you can check first.

Root Causes

Common causes of a Thetford Style II not holding water in the bowl include a worn or damaged ball seal (use correct part for your model - verify with dealer), which typically costs $15-25. This rubber seal creates the watertight connection between the ball valve and the toilet base. Over time, the seal hardens, cracks, or gets damaged by chemicals or debris, allowing water to slowly leak out of the bowl.

However, your water loss could also be caused by the ball valve itself being warped, cracked, or not seating properly due to mineral buildup or debris. The valve mechanism spring may also be weak, preventing proper sealing pressure. Additionally, the ball valve guide or the seat where it rests might have calcium deposits or damage preventing a tight seal.

In some cases, using harsh chemicals like bleach tablets can cause premature seal failure, while hard water areas see more mineral buildup issues. If your RV sits unused for extended periods, seals can dry out and crack, especially in extreme temperature conditions.

Before You Start

SAFETY WARNING: Always turn off water supply and wear protective equipment when handling waste system components.

Before removing your toilet, try this diagnostic test: Add water to the bowl and watch how quickly it drains. If it empties within minutes, you likely have a seal problem. If it takes hours, you might have a minor seating issue. Also, try gently pressing down on the foot pedal while the bowl has water - if the leak stops, your ball isn't seating properly rather than having a bad seal.

Check your toilet's manufacture date (usually stamped on the base) because Thetford made some design changes over the years that affect seal replacement procedures. Different Style II model years may have varying mounting configurations - check manufacturer specifications for your specific model. You'll need basic tools: adjustable wrenches, channel locks, a putty knife, new rubber toilet seal, and possibly a toilet flange extender depending on your floor thickness.

Purchase the replacement seal kit (correct part for your model - verify with dealer) ahead of time, as well as a new rubber toilet seal since you'll be removing the toilet anyway. Consider getting the entire valve assembly (correct part for your model - verify with dealer, about $40-60) if your toilet is over 10 years old, since the ball valve itself often needs replacing when seals fail.

Plan for this to be a 2-3 hour job if you're experienced with plumbing, or 4-6 hours if this is your first toilet removal. Have a helper available since RV toilets are awkward to maneuver in tight spaces.

The Repair Process

SAFETY WARNING: Always shut off water supply and disconnect all electrical connections before beginning work.

Start by shutting off the water supply and completely draining the toilet by holding the foot pedal open and pumping the flush mechanism. Remove the water supply line (usually a 3/8" connection behind the toilet). Use a putty knife to scrape away the caulk around the toilet base, being careful not to damage your flooring.

Remove the two or four bolts securing the toilet to the floor flange. These are typically 1/4" bolts that may be corroded, so penetrating oil helps. Carefully lift the toilet straight up and set it on its side on a padded surface outside your RV. The old wax ring will be messy, so have plastic bags and rags ready.

With the toilet removed, you'll need to access the ball valve mechanism from inside the toilet bowl area. Remove the ball valve assembly first to access the ball seal, which sits in a groove around the valve seat. Carefully pry out the old seal using a plastic tool to avoid scratching the seating surface. Clean the entire area thoroughly with denatured alcohol to remove any residue or mineral deposits.

Install the new seal by pressing it evenly into the groove, ensuring it's seated completely around the circumference. Reassemble any retaining components, then reinstall the toilet with a new wax ring, making sure it's level and properly aligned with the flange before tightening the bolts to manufacturer specifications in a criss-cross pattern.

Professional Help Needed

Consider calling a professional if you discover the toilet flange is damaged, cracked, or sits too low relative to your finished floor. Flange repairs often require cutting into the RV floor and may involve structural work beyond typical DIY comfort levels. Mobile RV technicians typically charge $150-250 for toilet seal replacement including parts and labor.

If you find multiple seals failing, have recurring seal problems, or discover the toilet base itself is cracked during removal, professional assessment is wise. Sometimes chronic seal failure indicates deeper issues with the toilet mounting, floor flex, or plumbing system that require experienced diagnosis. Additionally, if your toilet is integrated with a complex waste management system or has electronic components, professional service ensures proper reconnection and testing.