If your dump zone is adjacent to any "open space" then dwarves will throw it over the open space instead of dumping it on the tile. They can do this diagonally I believe, and there's some priority so they'll tend to always pick the same tile if there are multiple options. The zone does not need to extend over the open space.
For dumping stuff inside your fortress, you can construct a multiple z-level chute by having a miner channel straight down. He can do this safely assuming he doesn't fall into a cavern or other open space (not using a staircase prevents introducing a security vulnerability). Then connect the chute to whatever z-level you want trash access, designate a dump square next to the open space, and enclose the whole thing in walls/door. As a bonus, put grates/hatches over the open space and connect them to a lever somewhere. Even if covered, dwarves will place the dumped items on the grates/hatches. When you pull the lever, all will fall down to the bottom of the chute, into a cavern, lava, atom-smasher, whatever. The benefit here is it gives you a second chance to rescue things that may have been misdumped before they're gone forever. If you use grates or put the lever for the hatches somewhere safe, this trash chute can save the fortress as a means of emergency drainage after a flooding accident.
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Topic: Dumping stuff off cliffs (Read 2847 times)