The Sun-Mar 2-to-4 inch vent pipe diffuser is a simple but effective device originally patented by Sun-Mar principals to aid updraft, resist winter freeze-up, and protect the vent from downdraft and weather.
2″ diameter Sun-Mar pipe is required for venting Sun-Mar electric toilets, except the Mobile model. This includes: Excel, Compact, and Spacesaver stand-alone toilets, and all electric models of Centrex central composting systems (whether 1 pint flush, or dry flush).
Sun-Mar composting toilet duct/pipe for Sun-Mar toilets is NOT hardware store PVC pipe. If you try to use regular PVC pipe to replace/repair part of your Sun-Mar plumbing or venting, it will NOT fit into the rest of the system.