I agree with it being kitsch , but please , stop being so arrogant . It won ' t help you when you need to convince people of an opinion you hold dearly <| sep |> Depends a lot on the truck . Some have a mechanical system to open and close the back hatch . It will also have a set of giant bolts with wing nuts to tighten and lock it . Most likely someone got lazy and didn ' t put these in place . While running the truck they arnt needed to suck . You are creating a vacuum inside the tank anyways . Then the sewage created off gasses . The pressure relief valve either failed or the mechanical mechanism had a lower failing point . Source . I unfortunately have been dealing with a lot of shit lately at work . <| sep |> Usually I pick the players who I think will score the most points .