There are three 1-1/2" PVC running underground between my pump/filter and the pool. Two draw water from the pool (one for the skimmer and one for the MD, main drain). They meet at a three-way Jandy valve on the pump filter basket. There are quick-connects (unions) as they emerge from underground to make disconnecting the pump easy. These each get a rubber stoppper.

There's also one that returns clean water to the three inlets in the pool. That's blown out and stoppered.

The reason for the quick plugging of the MD line is once you stop blowing the air, the water will obviously be forced back thru (to a level even with the level of the water in the pool). It's not foolproof, but I'm not comfortable with the idea of antifreeze in my pool water either.

That help?