The Danco? trap vent prevents sewage from flowing back into the dishwasher. When water flows through the drain hose, it creates a suction on the water still in the dishwasher. The trap vent, makes a hole for air to get in. That way, the water only leaves the dishwasher when it supposed to, when it is pumped out.

Canplas P-Trap, Nominal Size: 3 in, Hub Connection, ABS, Black

Canplas Adjustable P-Trap with Union, Nominal Size: 2 in, Hub Connection, ABS, Black

Canplas P-Trap, Nominal Size: 2 in, Hub Connection, ABS, Black

Thrifco Plumbing P-Trap, Nominal Size: 1-1/2 in, Hub Connection, ABS, Black

Canplas P-Trap with Union, Nominal Size: 1-1/2 in, Hub Connection, ABS, Black