Defining the Boundary conditions of a 2-phase-flow (VOF)

Dear all,

I would like to simulate a two-phase-flow through a porous structure for my PhD similar to the two examples “dambreak” and “falling droplet”.
It is no problem for me to read an stl-file, define the two lattices of liquid and gas and also it is no problem to punch gas bubbles in the domain or even define “punching areas” by an own functional.
Now I would like to create an inflow condition for the fluid phase and a corresponding outflow condition for both phases (pressure boundary condition). What is the result are pressure and velocity “waves” going through the domain. It seems that I did not define the boundary conditions correctly. It is also curious, that there are negative pressure values.

So is it the right way to
… define the boundary conditions for both lattices?
… define the conditions like in poiseuille.cpp?

Or did I make a general mistake?
I would appreciate any short hint.
Thanks a lot in advance!