How to avoid Reversed flow at outlet
 

Hello everyone. I'm trying to simulate the water flowdown from a surface. I doing a multiphase simulation .Initial conditions are like the suface is covered with 1mm thickness of water and rest of the domine is filled with air. The inlet conditions are 0.05m/s and outlet is pressure outlet only the air comes out not the water. While running the simulation the there was a reversed flow at the outlet. How can i avoid this reversed flow. could you give me some suggestion to avoid this case.