Sealing hole around tubing to enter side window of tissue culture cabinet - (Aug/22/2014 )

Below are pictures of the side windows of a couple of tissue culture hoods. There are capped holes in both windows, presumably to allow tubing to enter. My question is how do you seal the space around the tubing with something that won't shed or leach anything that might affect the cell cultures?

The answer is with a "bung". Usually these are made of some sort of rubber or plasticized rubber, and if they are not wet, shouldn't leach stuff.