Simulating particles & liquid in a cyclone

[JuhaHo]

I got one idea, where I try this object test. My intention was to remove the Fluid force once the stones get near to the junk trap. Then the fluid force wouldn't prevent them from dropping to junk trap. Well, it doesn't work at all.

Can someone take a look, what I'm doing wrong here.

I made another test with this approach and it didn't got any better. Could someone please explain how this should work? This one is a disaster.