I just asked her that very question, as I have a holding tank with lots
of "residue" in it that prohibits an accurate reading of its level. She
suggests putting some Wisk detergent in it to slosh around and clean up
the greasy residue so that i can see how much stuff i have in it.

It will be easier in my trailerboat or another that moves around a lot,
but should still be an improvement, I think. At least it's a cheap fix,
even if it doesn't work.

Capt. Jeff