RV Tank Sensor Removal Guide: Gray & Black Water Tank Sensors (Step-by-Step Process)

The Rundown

Based on your description of finding sensors mounted under your RV tanks, you're most likely looking at external tank sensors rather than the more common internal probe-style sensors. These are typically either ultrasonic sensors that mount to the outside of the tank or magnetic float sensors that use external magnetic coupling through the tank wall. Without seeing the specific image you mentioned, the removal process will depend on whether they're threaded fittings that screw into external mounting brackets, bracket-mounted sensors held with screws or bolts, or adhesive-mounted ultrasonic units. Most external sensors are designed to be removable, but the method varies significantly between manufacturers like SeeLevel, Garnet, or Dynatek systems.

Why It Happens

External tank sensors became popular because they avoid the major drawback of internal probe sensors - the buildup of waste material that causes false readings. Unlike internal probes that extend into the tank and get coated with toilet paper, grease, and waste residue, external sensors read tank levels from outside the tank wall. However, they can still fail over time due to corrosion of mounting hardware, water infiltration into sensor housings, or calibration drift from temperature changes and tank flexing.

Many RV manufacturers switched to external systems because they're easier to service without draining tanks, and owners don't have to deal with the notorious inaccuracy of fouled internal probes. The downside is that external sensors can be more expensive to replace and may require specific calibration procedures when installed.

Gather These Items

• Socket set or combination wrenches (typically 10mm, 13mm, or 1/2 inch depending on mounting bolts)
• Screwdriver set (both Phillips and flathead)
• Digital multimeter for testing connections
• Wire strippers and electrical tape
• Penetrating oil (PB Blaster or similar) for corroded fasteners
• Silicone sealant or tank putty for sealing new sensor installations
• Safety glasses and work gloves
• Flashlight or headlamp for working under the RV

The Fix

Start by disconnecting power to the tank monitoring system at the monitor panel or battery connection to ensure electrical safety. Then take photos of the sensor wiring connections before disconnecting anything - this will save you headaches during reinstallation. If you're dealing with threaded sensors that screw into external tank fittings, draining the tank is not necessary since external sensors don't penetrate into the tank contents. Apply penetrating oil to any corroded threads and let it work for 15-20 minutes before attempting removal.

For bracket-mounted sensors, remove the mounting screws or bolts carefully, as the plastic tank walls can crack if you apply too much torque. The sensors typically have 3-4 wire connections: power, ground, and one or two signal wires depending on whether it's monitoring one level or multiple levels. Disconnect these wires at the sensor end, not at the panel end, to preserve your existing wiring harness.

If you're replacing ultrasonic sensors that are adhesive-mounted to the tank bottom, use a heat gun or hair dryer to warm the adhesive before attempting removal. Work slowly with a plastic putty knife to avoid damaging the tank surface. Clean all old adhesive residue with adhesive remover before installing new sensors.

When installing new sensors, follow the manufacturer's calibration procedure exactly. Most external sensors require you to calibrate them with the tank empty, then again at known fill levels. This process typically involves holding buttons on the monitor panel while the system learns the sensor readings at different levels.

Know Your Limits

While external sensor replacement is generally a DIY-friendly task, there are situations where you should call a professional. If you discover that your sensors are integrated into a complex SeeLevel system with multiple sensors per tank, the calibration process can be tricky and may require specialized tools. Additionally, if you find that the sensor mounting points on your tanks are cracked or damaged, attempting repairs without proper tank repair experience could lead to leaks.

Also be cautious if your RV uses a proprietary sensor system specific to your RV manufacturer. Some high-end coaches use custom sensor arrays that require dealer-specific replacement parts and programming procedures. If you're uncomfortable working with the electrical connections or if the sensors are mounted in hard-to-reach locations that require removing other components, it's worth having an RV service center handle the job to avoid potential tank damage or wiring issues.