Coolant Heat Reserve Tank Issue/Question

Ok. So I am refilling the coolant in my 08 Prius. As described in other threads, I am using the Lisle Funnel and manually running the CHR pump by jumping the relay terminals.

So, here is the problem.

When the pump starts running, the coolant starts cycling and the level in the funnel drops significantly. But when I stop the pump, all the fluid comes rushing back with significant pressure behind it. It is almost jumping out of the funnel, and the level returns to where it was before activating it.

Is this normal?