There is a “field test kit” briefcase thing that has swabs that if I remember correctly are paper with a little adhesive. After wiping around in the vent (behind the grate) you can lay it on a paper towel and spray with the field test kit spray. In less than 10 mins it will change colors according to the present drugs on the swab that the spray is rated for.
Source: my memory from me doing it ~6 years ago.
Well, I didn’t want a meth lab requiring me to replace all the drywall. Having the seller get scared when their sweet tenant left marijuana residue everywhere was a side effect that allowed better negotiation. Shrug, I was just doing due diligence, and the seller (via the tenant) left a few things I didn’t actually realize were problems until later: a section of uninsulated attic that was unclear without actually crawling in it (my inspector didn’t do it), a 240 volt oven whose breaker melted and was only supplying 106 volts, and dog pee infested 2nd story subfloor needing carpet to be ripped up and the floor sealed with paint. Also within 1 year of purchase I had both the shower tub crack and leak into the walls which was both an insurance call and a “restoration company” call, and not 6 months later, a sewer pipe for a sink broke inside the wall. I then said let’s sell this place. So shrug, negotiations only go as far as the info you know.
