flip turn with the Powerbreather
As you approach the turn, breathe normally through your mouth. Take a breath in before you begin the turn.
As you are rotating and flipping over, breathe about 20% of the air out gently through your nose.
As you push off, gently exhale the remaining 80% of air through your mouth once you are in facedown position.
Exhale mainly through the mouth.
Less experienced swimmers often do not realize that they mainly exhale through the nose when making a flip turn. People who do that will always find water in the D-Tubes when getting back to the surface.
Once you get the hang of it, you will not want to do flip turns with any training equipment other than the Powerbreather.