Fix RV Black Tank Sensors Reading Full When Empty - Easy DIY

Tools & Parts Needed

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What's Happening

Black tank sensors that read full after dumping are typically caused by waste buildup coating the sensor probes inside your tank. This prevents them from accurately detecting liquid levels. The solution involves cleaning the sensors using specialized tank cleaners, enzyme treatments, or mechanical methods like the ice cube technique.

Prep Work

• RV-safe toilet paper
• Tank sensor cleaner or enzyme treatment
• Water hose with tank rinse wand
• Rubber gloves
• Safety glasses
• 10-15 pounds of ice (for ice cube method)
• Dawn dish soap
• Calgon water softener (optional)

Your Action Plan

Method 1: Chemical Cleaning

1. Empty and flush your tank completely using your RV's tank flush system or a rinse wand
2. Add 2-3 gallons of water to the empty tank through the toilet
3. Pour in tank sensor cleaner following manufacturer's instructions (typically 1-2 bottles for heavily coated sensors). Ensure adequate ventilation when using chemical cleaners in enclosed spaces
4. Let the solution sit for 12-24 hours to break down buildup on sensor probes
5. Drive your RV for 10-15 minutes to agitate the cleaning solution
6. Dump the tank and rinse thoroughly with fresh water
7. Test sensors by adding known amounts of water and checking readings

Method 2: Ice Cube Method

1. Ensure tank is completely empty and add 1 gallon of water
2. Add 10-15 pounds of ice through the toilet (adjust amount based on tank size to avoid overloading - excessive ice weight can damage tank mounting hardware)
3. Add 1 cup of Dawn dish soap and 1 cup of Calgon water softener
4. Drive for 30-45 minutes over varied terrain to create agitation
5. Let sit for 2-3 hours for ice to melt and soap to work
6. Dump and rinse tank thoroughly
7. Check sensor readings with fresh water test

Method 3: Enzyme Treatment

1. Add enzyme-based tank treatment to empty tank with 2 gallons water
2. Allow 24-48 hours for enzymes to break down organic buildup
3. Agitate by driving periodically during treatment period
4. Dump and flush tank completely
5. Verify sensor accuracy with water level test

Know When to Call for Backup

Contact an RV service technician if sensors still read incorrectly after multiple cleaning attempts, if you notice tank damage during inspection, or if electrical connections to sensors appear corroded or damaged. Professional replacement may be needed if sensor probes are physically damaged or if the monitor panel itself is malfunctioning.

Keeping This From Happening Again

• Use only RV-approved toilet paper that breaks down quickly
• Add tank treatments regularly with enzyme or bacterial additives
• Rinse thoroughly after each dump using tank flush systems
• Perform monthly sensor cleaning during heavy use periods
• Keep adequate water in tank when using to help waste break down
• Avoid putting grease, oils, or harsh chemicals down the toilet
• Use tank treatments before storage to prevent buildup during non-use periods