Yes you can, 2" vent pipe can handle up to 20 fixtures as long as the vent pipe length is 50' or less for a 1 1/2" waste line and the tie-in has to be 6' from the waste trap.

That said in most cases for something like this most use air admittance valves to vent these filters.

She's not asking if she can use the vent pipe as a vent. She's asking if she can have the filter drain into the vent pipe.

I'd guess that it probably isn't allowed by code (although I'm no pro).

Hi. Yes, I am asking if I can use a vent pipe to drain water from the iron filter. In the attached picture, the vent pipe is the white one that goes across the top. The plumber who is installing the iron filter says "yes." I'm just looking for third party corroboration before I pull the trigger. Thanks.