If you need to drain below the return, this works well for me:
Place the vacuum adapter into the skimmer with the hose and vac head attached and in the pool.
Get your garden hose on a gentle flow and point it into the skimmer - this will give you a good seal around the vac adapter.
Put your filter to drain or rinse and turn the pump on.
This will allow for you to drain your pool to whatever level you desire.