I forget where but some youtube vid which pretty much just says they're not looking for small amounts, it's really explosives/weapons they give a shit about, large amounts of drugs too sure, but they're not geared up for tiny amounts. IIRC all the swabbing they do is for explosives but I might be wrong.
many years ago (early 2000s so may not still be as relevant), I once had a trip out to amsterdam and 1 muppet I was with didn't do the usual toss what's left, they just took it through in their pocket.
a flight from Amsterdam to London is literally the 1st place you'd be checking for drugs, none of use knew, couldn't believe it when he skinned up a joint in the car on the way home, everyone was like WTF did you do?! Still not sure if he was just cucumber cool or so baked he thought it was a good idea. I seem to remember Schiphol airport even had amnesty boxes before security.
Please don't do stupid things like this, very dumb thing to do.
but anyway they ain't picking up trace amounts, and even if they did if you're clean the very very worst you're getting is a delay for an anal probe