When I create a Stable room, I try to set the number of Smog Slug and Plug Slug I want to see in this room.
I use two Critter Drop Off. One to set the number of Smog Slug and an other to set the number of Plug Slug.
But the game count all Slug for rach Critter Drop Off
Build two Critter Drop Off in one room.
Set the filter on each one in a different variant of the species