Hello, Long story short. My fresh water tank has a hard grit of some sort in the bottom of the "V" form. I used to think it was a coarse sand, except that I can crush the granules with my fingers. When the water gets stirred up, the grit gets carried to the fresh water pump and caused problems so added an inline screen but now the screen gets clogged. Perhaps some precipitate (undisolved substance) from the fresh water "purifying" tablets? It's really annoying, as my FW tank is looks like an inverted pyramid, fitting into the "V" hull space beneath the "V" berth, and I could see the bottom of the tank has what looks like about a quarter inch deep of this stuff. The stuff sort of resembles the chemical called "Speedi-Dry", an oily floor absorber, also used by some for "Kitty Litter", but smaller granular sized. Has any one else seen stuff more / less getting into their water tank ? I just wonder if another chemical might be added to dissolve it and just flush the tank out? Another part of the problem preventing a complete tank flush, is that the drain outlet is about 1 inch off the bottom of the tank, preventing just "draining" it out. Tipping the tank up is really awkward, since it's tightly mounted inside the boat!. Bob E s/v Second Nature "..... may you always find fair winds, good sailing and a safe harbor"