Sensors

Use an alkali to get rid of soap scum. Sodium hydroxide if you know how to be safe with it otherwise sodium bicarbonate.

the sensors (well the cheap factory ones) activate the light when there is a lower resistance to ground. normally water provides the low resistance path. But so does soap scum, grease, food etc. The sensor circuit looks for an open circuit (infinite resistance) or a resistance in the 10's of kohms. doesn't take much scum or junk on the end of the sensor tip to meet the lower resistance threshold.

My parents rented out a small apartment upstairs. One lady lived there for three years, she never washed the shower stall. Dad ended up tearing it out to replace it, that's how dirty it was with soap scum.

I never even look at those sensors anymore. I know how many days until I have to dump and just plan accordingly.

It's the same reason that bathtubs get really nasty if you don't clean them, or that your kitchen sink trap sometimes needs cleaning.

Contrary to the commercials, one drop of Dawn Dishwashing Liquid does not remove the grease from a 35 gallon tank of sludge.

What does help is to take that tank of sludge for a bumpy ride, then dump, refill, and dump again. This will do more to keep tanks clean than about anything else.

Bob Vaughn wrote:
I understand why the black tank sensors get fouled but cannot understand how the shower and the kitchen sink tank sensors get fouled as soap is supposed to clean things so what is the cause?

Soap can leave film on the sensors affecting how they are functioning.

Soap scum residues, oils (body & cooking/foods), hair etc etc

Grey can be nastier then black due to the 'debris/stuff' that goes in and accumulates.