I usually remove the safety caps and stuff them in the seats at movie theatres.
Seriously, since I'm a paranoid fucker, I dispose of my pins in a plastic, non see through laundry detergent bottle. I crush amps/bottles and blister pack foil, etc and stuff them in the bottle too. Then I glue the top on the bottle with epoxy and throw it in a commercial dumpster in an alley somewhere. Although I doubt it could ever happen, I'd worry about some dumpster diver opening up my garbage and accidentally pricking themselves. Then they go into panic mode, call the po po and get fingerprints off the darts tracing them back to me. Paranoid, and very unlikely to ever happen, I know. But the time and extra effort involved is worth the piece of mind IMNSHO.
BTW-my friend was being watched by the cops for AS dealing. He threw away a few pins and a couple empty t-bottles in his garbage can behind his house one night which was enough evidence for the cops to get a search warrant for his house. He got caught with 4 bottles of supertest and the cops threatened to arrest his wife, have his kids taken away, etc. if he didn't cooperate with them. His case is still pending.
FYI-if you're being watched by the po po, they can and will legally go through your garbage nightly before they'll ever tap your phone, follow you around, etc.