This is a Foam Trap designed to capture any foam/liquid electrolyte. If during driving foam buildup or splashing may cause electrolyte to get into the tube that goes to your engine. Without the Foam Trap, there is nothing to prevent electrolyte from getting into your engine, and protect you from costly damage or repairs.
This design is easy to install and to empty. Just cut your hose and insert inline. If liquid is found in the trap, just unscrew the bottle and pour it back into your reservoir. A must have for any HHO enthusiast.