You have aparently a leak somewhere. Go through your equipment step by step and check if something isn't tight.
My guess is with DeSade though. I bought a pussy pump for my slave and no matter how much we tried we could impossibly get it air-tight. She was very slim and in good shape so I'm guessing that she didn't have the physical requirements for it. I think we needed a silicone sleeve or something. But we never got that far.