Dometic/Sealand’s Eco Holding Tank Vent Filter (311004) is an updated universal vent filter than can be used for new installations or as a replacement installation for all previous sizes of the Sanigard vent filters. This newly designed vent filter channels malodourous gases through its charcoal media, making it more effective at odor elimination for vertical and horizontal installations. This filter uses 55% less plastic than previous models for an environmentally friendly design. The Eco Holding Tank vent filter comes with fittings for 5/8", 3/4", 1" and 1 1/2" hose inside diameter. One size fits all.Previous part number 309311001 is replaced by this new number (same filter).