Every year my city does a clean up day - put anything on the curb and they will take it away (hazardous waste needs to go to a special collection location not the curb). All the scrappers know that day and will be driving around trying to beat the trash trucks to anything good and as a result most of the "trash" doesn't get to the dump.

People do put things on the curb other times of the year, but a dedicated clean up day helps everyone - you know when it is your turn, and the scrappers don't waste gas driving down dead end streets.