From sampling to weighing, an EPA procedure outlines every step.

Anytime you have a distributed sampling regimen—distributed in time, space, or both—it’s important to have a well-defined sampling procedure to ensure continuity for the whole operation.  This standard operating procedure describes the steps necessary to sample Great Lakes water for total suspended solids.  After sampling at given depths and locations, the water is pushed through filter papers, where the solids are collected.  To get an accurate measurement of the total solids, the filter paper is weighed with an accurate instrument: an analytical balance.  The document also mentions safety concerns in a nice practical fashion: “common sense and good judgement(sic) should dictate appropriate safety gear.”