Pressure BC on pool top
 

hi,
I new to fluent. Iam doing a 3D simulation in which there is a reactangular pool and there is inlet pipe distributing flow inside the pool and an outlet pipe is sucking fluid from pool. Inlet BC: velocity inlet, Outlet BC: Pressure outlet, pool is of 8.5 m height and is at 1.5 kg/cm2 pressure, how to give that pool top pressure. Fluent is taking as wall by default if we are not giving ant BC.
Please let me know how to do this