Fluid Flow between small pipe and large tank

This may be a simple question:

I have a small vertical pipe with an inlet at the bottom (inlet velocity =~10m/s). The pipe is connected to a larger tank at the top. The outlet is set to be at the top of the tank and that edge is at atmospheric pressure. How do treat the connecting boundary so that fluid will flow from the smaller pipe into the larger tank? Currently I have chosen to ignore the small edge at the top of the small pipe that is in contact with the tank but the solution will not converge. It is laminar flow problem and I have had success when just modeling the pipe (making the top of the pipe at atmospheric pressure). Any ideas?
Thanks!

Amber