A picture paints a 1000 words, now I understand, the tank is drilled as is the intake pipe hence the concern over the airLoulou;1930230; said:In fact I have drilled the intake tubes for the cups... below is a picture showing these intakes (the tube in the middle is for the air lines)
So, as the water level goes down during a change, at one point it will reach the place where the suction cup is - and where the hole that I have drilled in the tube to hold that said cup is. My concern is that air would then go into the intake... though that remains to be tested.

I can't see it being too much of a problem, your only looking at, if it leaks a tiny amount of air