Problems with BC's for two phase flow

Dear All,
I am a newbie simulating things with LB. I started with xFlows some time ago, but now I have problems with bc’s for two phase flows. I changed the rayleighTayler2D setup in that way that two phase-columns are present, one driven down by buoyancy.
At the outlet i used a setVelocityOnBlockBoundaries ( boundary::dirichlet), then setBoundaryVelocity and afterwards initializeAtEquilibrium.
This gives me a velocity at the outlet, that works, but this way I cannot get a “normal” outflow => Pressure =0. If I take the setBoundaryPressure, i have to define a density, and by defining a value of “1”, I get a flow inside the domain. To set a pressure level there would be very good. Does anyone know if this is possible?
Additionally I was not successful in adding an (velocity-)inlet.

Perhaps anyone can help me,
Thanks in advance,