This video discusses the addition of a gate Valve at the end of the waste stack to avoid drips collecting in the end cap of the waste stack. Over time we have discovered that residual fluids will collect between the tank shut off valves and the end cap. This pipe is closed at both ends, tank valves and end cap. When there is a pressure differential between ambient air and the air in the pipe, when you remove the end cap to place the waste pipe on you can get an unpleasant surprise as that pressure is relieved.
Now a waste hose can be attached prior to releasing and pent up pressure in the waste stack.

https://www.valterra.com/product/twis...

https://www.amazon.com/CamcoSewerHo...