Replaces the original termination cap on Thetford Slide-EZ sewer waste valves. Fits Thetford proprietary 3-3/4" sewer fittings. Stores in standard 4" square bumper while attached to 3" sewer hose. For Thetford-standard sewer systems used on vintage and older RVs. Does not fit modern Valterra bayonet fittings.
The Thetford 01664 is the replacement termination cap for the Thetford Slide-EZ sewer waste valve — the proprietary sewer connection system Thetford used on RVs from the late 1960s through the 1990s. It replaces the original cap that seals the sewer outlet when the hose is disconnected, preventing odors and protecting the valve fitting during travel and storage.
The Thetford sewer standard uses proprietary fittings sized to fit around a 3-3/4" pipe — different from the modern 3" bayonet system used on contemporary RVs. As a result, the 01664 does not interchange with modern Valterra-style bayonet caps and is specifically a part for older RVs still running the original Thetford Slide-EZ valve system. The cap fits inside a standard 4" square trailer bumper for storage while still attached to the 3" sewer hose — the same convenient storage method used with the original cap.
• 1x Thetford 01664 replacement termination cap Other Thetford Slide-EZ sewer valve parts: • 08669 / 08706 / 08707 / 08709 — Thetford Slide-EZ waste valves (various configurations) • 09872 — Slide-EZ valve repair kit (all-plastic valves) The Thetford sewer standard is no longer used on new RVs. These parts are primarily needed for vintage and older trailers built before the 1990s.
Thetford's proprietary sewer system was the dominant RV sewer standard from the late 1960s through the early 1990s, used by many manufacturers. It uses fittings sized around a 3-3/4" pipe with an O-ring connection — different geometry from the modern 3" bayonet system that became the industry standard. Because the dimensions don't match contemporary fittings, vintage trailer owners need to source Thetford-specific caps, valves, and hose fittings rather than modern replacements. Most RV shops don't stock these parts, making specialty suppliers the primary source.
Despite how this product is described in some listings, the Thetford 01664 is a sewer waste valve cap — not a toilet seat cap, toilet lid, or any interior toilet component. It caps the exterior sewer outlet fitting on the Thetford Slide-EZ valve. It also does not fit modern Valterra-style bayonet fittings used on RVs built after the early 1990s. Confirm your RV uses the Thetford proprietary sewer standard before ordering.