I used to do that, back in the 90s in college.  First I just put tons of trash paper in business-reply envelopes and drop them in the mail, then I started filling them up with gravel.<p>Years later, on the internet, I remember seeing some article about people doing this, and they had pictures of things like business-reply envelopes attached to bricks, which the USPS had received.  IIRC, they said that the USPS didn&#x27;t actually send these or charge the business for them, unfortunately.<p>So stick with just dropping them in the mail as-is, to make sure the business gets charged for it.