VOF outflow of settling tank
 

Hi, I'm simulating a settling tank with VOF. the tank has a volume of 300 cubic meter. The inflow=0.2 m3/s and it should thake around around 1200 second till fluid reaches the outflow. But I get the outflow after 800 s, which means after 80 m3 inflow.
It just does not make sense, does anyone has an idea why is like that or what does that mean?
Thank you in advance