Air vents, porosity, selective outlet
 

I want to simulate the filling of a small channel (aprox. 65mm length), with 3 "T" ramifications with a fluid of high viscosity (200 Pa.s). Because of the difficulty of simulate air vents, because of their small dimensions, I'm thinking in other solutions to allow the escape of air but not of the viscous fluid. Can anyone give me some ideas? Can I use porosity to do that? How? I'm also thinking if there is any way to establish a "selective" outlet, only for air?

Thanks, Catarina.