Julie Bove wrote:

> I've cleaned the inside of my tank at some of the places I've lived.
> Sometimes it gets really mucky in there. Sometimes not. Not sure what
> causes it.

It is probably mostly particles of dirt from your water supply. Municipal water
is pretty clean, but there is still some stuff that gets through. I get water
from my well and the soil here is sandy loam, so there is a brownish sediment
that builds up rather quickly. Ever month or so I stir it up and give a few
flushes to purge it from the tank.