You need to take the system out of the airplane, connect everyting up and submerge the system in water. Pump the system up and see wherethe air bubbles are coming from.I had a similar problem with a brand new Robart setup and found that the fill valve was leakingbadly. No matter what Idid I could not get the valve to seal after removing the air pump fitting, I ended up replacing the brand new valve and my air leaks stopped.