Dump valve

A dump valve is a slide (gate) valve with a large T-handle that opens the discharge of a grey or black holding tank into a dump station. Standard US size is a 3″ (76 mm) port; European systems use 1¼″ or convert via an adapter.

Standard procedure: open the black valve first (so solids settle in the rush of water and clear out fast), then the grey valve (which rinses the sewer hose of odours). Brands: Valterra (US standard), Thetford, Fiamma. After 1–2 seasons the seals leak — replacement costs $10–15 and takes about five minutes. A jammed dump valve is a classic winter failure: ice deforms the slide. Cure: warm the tanks and apply WD-40 on the rails.