Happens to all of us.
When I change my 180/100 gallon system that houses a lot of my big catfish I use a wide diameter hose in order to be able to drain enough water. (A python would take forever to do the 50% water change necessary to keep all those dirty catfish healthy.) Anyways, I got a nice big lungfull of water. Turns out you really just get the technique down quickly once you've learned the hard way. 
Now no more sucking guys.