I can't figure out what is going on - when I attached my suction line vacuum (zodiac mx-8) properly air enters system. This particular vacuum comes with a gauge to test vacuum pressure. I decided to use the gauge so first had to insert a 4 inch tube apparatus into the skimmer hole (all underwater by 8 or more inches) with the pump perfectly primed, immediately I saw a small tornado and tons of air entered pump basket and prime was lost - when I removed the small tube the system was able to reprime itself. I thought it had something to do with the vacuum but now I am really confused how could just inserting a hollow tube make air enter the system???? Any help or ideas would be very much appreciated.