You need two things. A 12" pair of needlenose pliers and a flashlight.
Use the flashlight to illuminate the underside of the intake, once lit you should be able to see the pipe nipple the line goes to. Once you see the nipple, it is simply a matter or using those long needlenose and a little finesse to slip the rubber back on the nipple. The long neddlenose let you reach way in under the intake, but check closely, you may have to pull the distributor cap to have enough room.
PS: all the vacuum ports should be on the port side of the throttle body.
'73 280SEL 4.5 (9/72)- RIP
Only 8,173 units built from 5/71 thru 11/72
'02 CLK320 Cabriolet - wifey's mid-life crisis
2012 VW Jetta Sportwagon TDI...at least its a diesel
Non illegitemae carborundum.