Homemade Tear-Gas Mask

Here is another technique I found in picture form.  It diagrams how to make a homemade tear-gas mask using a 2 liter (not litre) soda bottle.  Looking at the instructions two items that you may not have lying around the house: a clinical mouth-cover and a strip of rubber foam.  Get the mask mouth-cover at any local pharmacy.  I'd check the local hardware store for the rubber foam seal.

As with any technique, practice & perfect before you really need to use it.