RV Vacuflush Toilet Odor Fix: Stop Black Tank Smells While Driving

Quick Take

The black water odors in your 2016 Fleetwood Bounder during travel are most likely caused by a failing ball valve seal in the Vacuflush toilet, allowing tank gases to enter the coach. This happens because of air pressure changes and vehicle movement while driving. The lack of a visible roof vent is actually normal for many Vacuflush systems - they often vent through the generator compartment or sidewall instead of the roof. The solution involves checking your vacuum trap water level, adjusting your driving habits, and possibly installing an additional vent or check valve.

Common Causes

Vacuflush systems are particularly susceptible to odor issues during travel due to their unique design. The most common culprit is the ball valve seal failing to create a proper barrier. Vacuflush toilets use a ball valve mechanism at the base of the bowl to block sewer gases, not a water trap. When you're driving, especially on hills or during acceleration and braking, this water can be forced out or siphoned away by pressure changes in the black tank.

Your Bounder's Vacuflush system likely vents through a sidewall fitting near the generator compartment or through the floor, rather than a traditional roof stack. This lower vent location can create pressure differentials during travel that affect the ball valve seal. Additionally, the vacuum pump can create pressure imbalances if there's insufficient venting or if the system's check valves are failing.

Temperature changes during travel also play a role. As the black tank heats up from road temperature and engine heat, expanding gases create pressure that seeks the path of least resistance - often through a compromised ball valve seal.

Preparation

Before starting any work, you'll need to locate your Vacuflush system components. Check the generator compartment and exterior sidewalls for a small vent fitting - this is likely where your system vents instead of through the roof. You'll also need to access the area beneath your toilet to inspect the vacuum trap and associated plumbing.

Gather these tools and supplies: a flashlight or headlamp, basic hand tools including screwdrivers and pliers, a small mirror for hard-to-see areas, and some RV-safe toilet paper for testing. You'll also want to have fresh water available and possibly some RV holding tank treatment on hand.

Plan to do this work when your black tank is relatively empty and you can test-drive the RV afterward. Having your Bounder's manual handy will help you locate the specific Vacuflush components, though the vacuum trap is typically directly beneath the toilet base.

Repair Steps

1. Locate and inspect the vacuum trap: Check the ball valve operation by observing the flush cycle. The ball valve should seal completely after flushing. If you hear air entering the bowl or notice odors, the ball valve seal may be compromised.
2. Test the ball valve seal: Test the ball valve seal by flushing and ensuring it closes completely. The ball valve seal is critical for preventing odors from escaping the black tank. If the seal is damaged, contact a qualified technician for replacement.
3. Check the vent system: Locate your sidewall or floor vent (often near the generator area). Ensure it's not blocked by debris, mud, or insects. The vent should allow air to enter the system to prevent vacuum siphoning of the trap water.
4. Test vacuum operation: Flush the toilet several times to ensure the vacuum pump is working properly. Listen for the characteristic vacuum sound and verify waste is being pulled down effectively. A weak vacuum can indicate pump issues that may contribute to venting problems.
5. Install additional venting if needed: If problems persist, consider adding a Studor vent (air admittance valve) to the system. This one-way valve allows air in but prevents gases from escaping, helping maintain proper pressure balance during travel.
6. Secure all connections: Ensure all plumbing connections are tight and properly sealed. Loose fittings can allow odors to escape and affect system vacuum performance.
7. Test drive: Take your Bounder for a test drive including hills and turns. Stop periodically to check if odors are present in the coach and listen for any air leakage sounds from the toilet area.

When to Get Help

Contact a qualified RV service center if you discover the vacuum pump is not functioning properly, as these pumps require specialized knowledge to repair or replace. The vacuum pump motor typically costs $150-300, while a complete pump assembly can run $400-600 installed.

If you find cracked or damaged plumbing components in the vacuum trap area, professional repair is recommended since improper sealing can create bigger odor problems. Also, if your research reveals that your specific Bounder model should have additional venting that's missing or damaged, a technician can properly install the correct venting system for about $200-400 depending on complexity.

Get professional help immediately if you smell propane along with the sewer odors, as this could indicate a dangerous leak. Similarly, if you find evidence of black water leakage in areas where it shouldn't be, stop using the system until a professional can assess potential health and safety hazards.