Chaff - cholesterol crystals. white translucent tiny, they float. This is how the body excretes excess cholesterol.
Gravel - probably precipitated minerals, calcium. It may be possible to disolve this using the methods of dissolving/softening stones. If the body is acid, not slightly alkaline, then minerals tend to precipitate. There are some prepartions for keeping the body slightly alkaline but I use diet. See acid and alkaline forming foods.
Sludge - could be a mixture of the above with thickened bile, bacteria and white blood cells, parasites. When sludge forms a gel or solidified it can be difficult to break it up so it will come out.