Link to Purchase: https://amzn.to/3oTawd8
Valterra 3" black bayonet cap, part #T1020BU. This part has many uses but it fits on the Valterra T80 sewer valve. The cap has a strap to hook it to a sewer valve.
Specifications:
Cap Size: 3"
O.D.: 4.125"
Reinforced ears for long lasting durability