RV Repair Manual
for the RV Do-It-Yourselfer
Standard RV holding tank monitor panels rely on simple stainless steel studs screwed through the side of plastic tank walls. When waste liquids touch a probe, electrical current completes a circuit to illuminate indicator lights on the monitor panel.
Unfortunately, toilet tissue, grease, and tissue sludge quickly coat probe tips inside black and grey tanks, creating false continuous continuity bridges. This causes monitor panels to show "2/3 Full" or "Full" even immediately after dumping.
Deep-clean fouled probes by adding a concentrated holding tank probe cleaner along with 10 gallons of water prior to driving. The sloshing motion during road travel scrubs grease and paper off probe tips.
If factory probes continue to short out, replace standard wall studs with domed Horst Miracle Probes designed with umbrella shields to prevent tissue buildup. Alternatively, upgrade your system to an external SeeLevel tank monitor system that adheres to the exterior tank surface and measures fluid levels digitally through plastic walls without touching waste.
Maintenance Tip: Never use petroleum solvents or heavy soaps in holding tanks – they strip natural probe coatings and accelerate grease adhesion.