All the information about compressors and nebulizer cups is baffling! I was using the old standard cup with a Power Pro Neb compressor, but the condensation would form inside the cups and would never stop misting. So after recommendations on this site I switched to PariLC Sprint cups which seemed to do okay. Then my cheap amazon travel nebulizer quit (not intended for saline) and I bought the PartTrekS in mid-May. Loved how quiet it was and seemed to work well, but now like Kate, it gets all foamy and only seems to completely empty when I attach Aerobika. Dr. Winthrop prefers that I do nebbing and Aerobika separately, unless I really need to hurry. I've tried switching to brand new cups. And also thought maybe it was being caused by exhaling into the cup, and tried to avoid that. It's actually kind of random, sometimes okay and then not.