Hayward S200KT Dome Wrench for S200 Sand Filters. The oldest and most popular method of filtration is sand. They operate on the basis of 'depth' filtration; dirt is driven through the sand bed and trapped in the minute spaces between the particle of sand. Initially, a clean sand bed will remove larger particles, and then, as the bed starts to load up, it will remove finer particles. Cleaning of the media, or sand bed, is accomplished through reversing the flow through the filter, to the 'waste' line.