Peter Scott wrote:
Interesting idea. Let us know if you can actually feel the boundary. My
neighbour could use this. They are desperately trying to avoid the cost
of a sewage plant like mine, but their septic is proving troublesome.

Maybe there's a market for an automatic indicator. You'd need to use a
float with a density that lies between the density of the sludge and the
liquid. Some guesswork or rather unpleasant measurements to make here.
My guess is that there wouldn't be much difference. Then you'd need to
calculate the float volume. This must be big enough that the difference
in density will give enough upward force for the indicator. Perhaps a
string wrapped round a geared dial. Hmmm. There's a programme on the
moron box for potential inventors isn't there? Bet they wouldn't have
this one on.

Don't forget to put on your snorkel and mask in case you fall in!

Hee, hee, hee. LOL. Exactly! I don't fancy it, but for me £120 a
year, needlessly, is worth saving. At the last place we lived, in West
Wales, in the middle of winter and therefore well padded in thick woolly
clothing I was pruning bushes close to the edge of one of our
six-feet-deep ponds . . . and I fell in, head first! The water was
ice-cold but clean and the experience was horrific! Falling into a
septic tank . . . well, I guess with the bacteriological action it might
actually be reasonably "warm", but certainly not clean!

Peter, you propose a gadget far superior to mine. Feel free to pursue
the idea - it will make a thrilling episode on Dragons' Den - even if
they do all tell you they're "out"!

Eddy.