Calculation of fluid flux

Dear all,

in older versions of comsol, there used to be a variable that one could integrate in order to get the fluid flow across a boundary, which was called something like flux (I can't quite remember its name).

How can I integrate the fluid flow rate (e.g. in Darcy's law module) in m3/sec across a model boundary in version 4.1?
There is no such variable called flux or similar.
Would dl.U be what I need?

Thanks a lot and best regards,
Juergen