If its a Theftford there was a faulty valve installed and they shipped mea replacement valve for free. I had the same issue as you. My TT is a 2010.
Joe, Joyce , 4 Kids and 3 Dogs.
2004 V-10 Excursion with Hellwig sway bar, Roadmaster Active Suspension, Bilstein shocks and steering stabilizer, Super Duty Tow Mirrors,
3.73 Gears, Reese dual cam, Prodigy brake controller.
2010 Jayco Jay Flight G-2 32 BHDS