This has to be done with at least two players no matter the connection. The first player must commit suicide or otherwise die, and the second player must stand near the vent (see picture) and wait for the first player to respawn. If done correctly, the first player respawns inside the closed off room. The second player outside must now commit suicide to be able to join the first player. This also works in the "n00b vent," which is a popular camping spot in Infection when playing Sword Base. Also, the "Green Vent Room" is closed off, but can be accessed through this glitch.