Contrary to the description this item is not used to raise the eco footprint (at least not that I saw). Instead it is used to generate infinite trash in the dumpster.
Let me explain, the smog vac can vacuum up one charge worth of "smog". You could do 2 things with that one charge
Option 1 Endure a loading screen and dump the smog somewhere else (loading screens make this less desirable)
Option 2 Dump that charge in a bin or dumpster to get the dive for interactions to appear whenever you want. (note you may need the recycle trait for the options to show up).
I prefer option 2 because I can place a dumpster on my lot and that one charge of smog turns into several charges of dive for interactions which is very resource efficient.
As i said the name smog vacuum is misleading don't try to use it to clean up the eco footprint, use it to get infinite trash resources.