Plastic inline backflow preventer (anti-siphon valve), prevents water from back siphoning into the main water lines and should always be used when applying fertilizer though Lawn Belt (via Micacle Grow bottle or similar). It has 3/4″ FHT on the inlet side with rubber washer, and 3/4″ MHT on the outlet side. Use this unit as the first component in your installation, and install it directly to hose bib and attach 3 foot hose to it.