Use the Watts WR100 filter wrench to loosen the bottom of the housing during cartridge replacement. Slide circular end over housing until a snug fit is achieved and unscrew. The Watts Flomatic WR-100 Wrench is a filter housing wrench for removing housing body from housing cap and is used for the replacement of filter cartridges. Do NOT use the wrench to tighten the sump. The Watts Flowmatic WR-100 wrench makes changing water filters easy. The Watts WR100 is a Sump Wrench for Residential/RV Housings.