The Flying Dumpster Glitch is a physics glitch present in Halo 3's campaign and Halo: Reach's forge and custom games. The glitch allows two players to fly a dumpster through the air by using timed jumps.
The easiest level to do this on is The Storm, at Checkpoint Alpha.
Two players should find an empty dumpster, tip it over, and walk into it. The two should then jump at the same time, jumping repeatedly to lift the dumpster into the air. If the two players are skilled enough, they can even steer their improvised aircraft and use it to attack the Scarab.
It is very easy to do in Halo Reach. First, start a forge game on Powerhouse and spawn a dumpster nearby a slope. Place it on its side. The opening must face down the slope or you will slip out. You need to be an Elite for this to work. Crouch into the dumpster with your friend, and look outside. Back up into the corner nearest to you. Both players should start jumping very fast. Attempting this with a single person rarely produces meaningful results, as the dumpster will only travel a small distance.