To prepare a schlenk tube we need:

- Rubber-band:

- Vaseline: 

- Silicon cap: 

The result will be this: 

References 

http://www.res.titech.ac.jp/~smart/facilities/Schlenk.JPG

http://www.area-integral.net/cat/img/OFICOMS28731.jpg

http://upload.wikimedia.org/wikipedia/commons/thumb/3/33/White_Petrolatum1.jpg/220px-White_Petrolatum1.jpg

http://img.alibaba.com/photo/543053661/butyl_rubber_stopper_for_blood_collection_tube.jpg