I used PVC pipe with a end cap glued on the bottom and a rubber cap held on with a hose clamp on the top. It is described here:
http://www.maverickexperiments.com/

The rubber cap on top serves well. I can blow into the tube and expand the cap slightly block the tube and see if there are any leaks. Or I can block the output and measure the time for the cap to change from concave to flat. Also in the event of an explosion ( I tested this) the cap comes off and the cell is not damaged.