6 Way Multiport valve with clear rinsing feature Sand filters must be backwashed in order to loosen up the sand and to eliminate filtered dirt through the waste system. This requires, among other things, that the hydraulic action of the filter circulation pump be reversed through the filter housing. These function as well as others can be adjusted easily and effortlessly with the BADU®Mat. The BADU®Mat is fully factory tested and together with the internal parts carries a 24 month ex-factory warranty from date of purchase.