I recently setup a DIY C02 injection system by doing the following:
        1) Dissolved 3/4 cup of sugar in 2 cups of hot water
           and poured this into a 2 litre bottle
        2) Added 3 cups of cool water in with the sugar water.
        3) Dissolved 1 teaspoon of yeast in 1 cup of warm water and
           then added this to the rest of the solution

I waited for a few hours until the solution began to bubble in a bucket.
I then connected this to a valve on the back of the tank.  From the valve,
I connect airline tubing with a bubble stone at the end of it.  

If I shake the solution, I get lots of bubbles in the tank.  However, if
the solution just sits there, I don't get any bubbles at all.  The aquarium
is in the family room in my basement where the room temperature is about
68 degrees.  I'm not sure why I get the bubbling in the test bucket, but 
not in the aquarium.  Could this be due to the cool temperature of the
room (i.e. the yeast is not active enough at this temperature).  

Also, the 2 litre bottle is below the tank on the bottom shelf of the 
stand.  Should I sit it on the lid of the tank?  I also noticed that
the yeast solution is not foaming like it originally was, and I have
tried two separate solutions over the past week with new yeast.  The
end result is the same - C02 in the bucket, but not in the aquarium.

Thanks in advance for any advice