Valterra Horst Miracle Tank Probes: Black vs Gray Water Parts

When an RV tank-monitor panel indicates that the black or gray tank is partly full after dumping, residue on the tank's level probes may be one cause. Valterra's Horst Miracle Probes replace compatible original electrical sensors and are designed to reduce incorrect readings caused by residue. There are different versions for black-water and gray-water tanks, and both of the kits below contain four replacement probes.

Compare black-water and gray-water probe kits

Why ordinary tank probes give false readings

Many RV level monitors use electrical probes positioned at different heights on the tank wall. As wastewater reaches a probe, the monitor detects a conductive path and indicates the approximate fill level. After a tank has been emptied, soap film, sludge or other residue can still form a conductive path between probes. The panel can then display liquid in the tank even when it has drained.

Horst Miracle Probes extend farther into the tank than typical button-style probes. Valterra surrounds the sensing section with a Delrin body and Teflon sleeve to reduce unwanted contact through deposits. The T21301VP black-water version also has a protective roof above the sensor to help prevent toilet paper from making contact. The T21302VP gray-water version addresses residue-related false readings in gray-water tanks without that black-water roof arrangement.

Replacement kits and photos

T21301VP — Black-water tank level probes

The black-water version adds a protective roof over the sensing tip to help prevent toilet paper from catching on the probe. Its longer, insulated sensing design also reduces false readings caused by residue bridging the sensor contacts.

View T21301VP four-pack

T21302VP — Gray-water tank level probes

The gray-water version uses the insulated sensing design to help reduce inaccurate readings caused by soap film, sludge and other residue in a gray-water tank. It is not the black-water version with the toilet-paper protective roof.

View T21302VP four-pack

How the probes connect to the existing system

This is a connection overview, not a wiring schematic for a particular RV. The location, number and connections of the original probes depend on the installed monitoring system. Follow the instructions for that exact monitor and tank.

What to check before ordering

1. Identify the tank. Choose T21301VP for black-water use or T21302VP for gray-water use rather than assuming the two sensing designs are interchangeable.
2. Check the existing monitor system. The kits are intended for compatible through-wall electrical-probe monitors. They are not replacement panels or solutions for unrelated external sensor strips.
3. Confirm the tank openings. Valterra specifies fitting existing 3/8-inch-diameter probe holes. Inspect the wall, seals and accessibility before replacing a probe.
4. Check the wiring. These replacement kits do not supply a complete wiring harness. Identify and label the existing wires before disconnecting them.
5. Prepare the tanks. Empty and rinse the tank, isolate the applicable monitor power and follow the probe-installation instructions. Ensure each probe is secured and sealed before returning the tank to use.
6. Verify operation. Check for leaks and test the monitor after installation. False readings may also be caused by damaged wiring or the monitor itself, not only dirty probes.

Related RV holding-tank references

For tank rinsing that may help remove deposits, see our Valterra holding-tank wand comparison and HydroFlush and Flush King guide. If the issue concerns drainage at the tank outlet, our waste-valve connection reference covers a different part of the plumbing system.

Identify tank-level probes separately from waste discharge parts