Well if air is getting into your lines, its more than likely the squeeze tube on your dispenser. but you should not rule out the sani. feed tube or the fitting at the machine (should be plastic). commercial sanitizer is very corrosive and will eat metal fittings to the point of nothing. worst case scenario, you have to replace all the tubes and fittings. on the sanitizer side of the dispenser. not a big deal and cheap.

hope this helps