Right place if you
Get false full, false empty, or stuck mid-level lights on black or gray tanks.
Water · plumbing
RV tank sensor troubleshooting
“Black tank always reads full” is one of the most common complaints — and it is rarely the monitor panel electronics dying first. Fouling and probe type drive most false readings.
Active corridor: Montana · Wyoming · Idaho · Washington — case-by-case beyond.
Field notes
On the corridor we see coated probes after a summer of under-treated black tanks, gray-film on sidewalls, and owners ready to replace the whole monitor because 2/3 lights will not clear. Clean first; replace second.
Who this is for
Maybe not yet if
You need dump technique — dump station. Treatment and odor — holding tank sanitation.
Probe vs strip (and external)
Internal probes
Screw-in or welded probes inside the tank. Great when clean; foul with paper and grease.
Strip / wand sensors
Often more forgiving but still coat. Follow maker cleaning guidance — do not scrape blindly.
External sensors
Some systems read through the wall. Wiring and ground issues mimic “bad sensors.”
Honesty
We will not invent a universal ohm table. Prefer Text a photo of the monitor and tank access if you want a visit diagnosis.
False full / false empty
False full usually means residue bridging probes or coating a strip. False empty can be a failed probe, open wire, or a tank that actually has a pyramid of solids below the lowest probe. After a careful dump and rinse, if lights still lie, clean before ordering a new board.
Clean methods that do not destroy sensors
- Use tank cleaners labeled safe for sensors; follow dwell time
- Ice or soft rinse methods some owners use — avoid anything that hammers fittings
- Never pour harsh drain opener or grind probes with metal tools
- Rinse thoroughly after chemical cleaners; leave water + treatment for the next trip
- Gray tanks: cut grease at the sink so sensors stay readable
What we see on corridor coaches
After storage
Dried film on probes reads full until a proper clean and wet cycle.
Under-treated black tanks
Paper bridges the lowest probes — treatment and rinse discipline matter more than a new display.
Gray film
Dish soap and grease coat sidewalls; sensor-safe cleaners plus sink habits fix more than boards.
Wiring chafes
Loom rubbed through near frames causes intermittent empties — Prefer Text photos before panel swaps.
DIY vs Prefer Text
Reasonable DIY
Treatment discipline, sensor-safe cleaners, verifying ground wires you can see, comparing readings after a known-empty dump.
Book us when
No tank access, wiring faults, repeated fouling after correct clean, or you want external sensor upgrades evaluated. Prefer Text monitor behavior in one short note.
FAQ
Replace the monitor panel first?
Usually last. Fouling and tank wiring explain most ghosts.
Fresh tank sensors?
Same idea — less sewage fouling, more mineral film; still clean gently.
After winterize?
Odd readings until tanks wet again are common — recheck after a fill/dump cycle.
Cost?
Prefer Text for a quote; trip/labor structure below. No invented part prices.
Related: Holding tank sanitation · Dump station · Toilet systems · Troubleshoot
Pricing teaser
Trip fee $75 within 30 miles, then $1.50/mi each way. Labor ~$150/hr (1-hour minimum, billed in 30-minute increments). Diagnostic $175 applied toward repair if you proceed.
Credentials (text): Victron Professional Certified Installer · weBoost Authorized Installer · Peplink Certified Associate · Dometic Professional Certified. Starlink = installs only (not a certified partner title).