You can use e-wall+fan

o.O?
How?

First, draw your fan and set-up it then draw an e-wall around your fan.


edit:
example here https://powdertoy.co.uk/View.html?ID=8855

yes but you have some workaround

You can use some detectors inside. E-wall will be open until the chamber is empty

outi
How do you set-up the fan? I can't seem to make the fan blow in the direction I want... =(

Ok, found how on the wiki ^^