Slow Sand Filter : A very large filtering unit containing said. The fluid flows through the sand bed very slowly because of the large bed size. Generally, these filters are too large to be economically practical. (SSWID)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}