Guys,
Yesterday I completed my 2nd flight on my Jet Legend T-45. At the time of defueling I realized that the wall of UAT compresses inward as I defueled. Like wise it inflates a little more than its normal shaps as I fuel it up. I have checked for all kinds of kinking and have also pushed air through the fuel vent that is coming out of fuel tank. It seams normal.... the fuel goes in and out of tank without any problem when pushing air manually my mouth. The problem starts as soon as I attach fuel pump to fuel and de-fuel.
Please let me know what could be wrond here.

Also there is no bubble coming in the fuel pump. There is no air leakage.

Regards
Asif