The donut fits ON the hole and you put a heavy weight on top of the elbow to press down...
Weights
1: Rock (most common) includes concrete block
2: Sand bag
3: Water bag
3:
http://www.hosebuddy.comScrew in is best but that works too
NOTE: some sewer dumps the smooth stepped adapter will seal well enough though I would not mind putting an "O" ring (or flat ring) on the thing to improve the seal (The ring should fit around the largest segment to fit in the pipe and seal to the top of the pipe.. Of course this assumes the pipe is in good condition)