Take the Teflon tape and wrap the threads of the air valve plug.
Install air valve plug into the front of the bottom drain valve.
Apply Teflon tape the standard plug.
Put that plug into the top of the drain valve.
Once you've done that, leave your top ball valve closed and open the bottom valve.
After you've done that, use anything that can pump air. Hook that onto the air valve and pump air through that until you see a regular flow of bubbles coming out of your bottom drain.