Check the listing for details. Dema Dema 16-30 Backflow Preventer. Condition: New. Listed at 21.99 USD. Garden Hose Threads (GHT, FHT, MHT) create a water-tight seal by using a flexible washer between the two connection pieces. Thread seal tape is not recommended since it can inhibit the full threading together of the pieces, thus not allowing a tight leak-proof seal. GHT are not compatible with NPT or IPT/IPS fittings commonly found in iron pipe or PVC water systems. The Dema model 16-30 Backflow Preventer is an ASSE 1055B certified Action Gap Backflow Preventer for Dema dispensing systems. The model 16-30 connects with 3/4" hose threads at the inlet and outlet. This backflow preventer is not rated for constant pressure and must be used downstream of any valves or timers.