Wouldn't it diffuse C02 better if you put it on the inflow instead of outflow?
Seeing as how the canister is air tight, or should be; that gives a longer time for the C02 bubble to be in contact with the water. Not to mention all the times it comes into contact with your pot scrubbers, egg crate, ect. will diffuse it even more into the water. It just makes sense to me.
I made a DIY canister filter out of one of those old Country Crock butter containers. I had the line from the C02 bottle running through my inflow, didn't seem to have any adverse effects at the least.