I have a question about closing pool. It's an inground pool and has Vari-Flow 710 handle and Hayward sand filter. I have one of those plugs that goes in the skimmer for winterizing and allows you to leave water level above skimmer. However the plug doesn't have a cap that can be removed. I will need to blow out the skimmer line from somewhere in the system and have someone else install the plug while I'm pressurizing the system with air. My question is in regards to the best way to blow out the line. My instinct is to set the Vari-Flow to Waste and blow air through the waste drain (which is currently not hooked up to any plumbing). This means air would flow backwards through the system starting at the waste drain and then traveling through the pump then the skimmer line. Is there any danger in air flowing backwards through the pump? Will this spin the pump the wrong way and damage it?