[davemonkey]

Grim is right about the glass diffuser requiring more pressure than DIY can provide (unless you have two large bottles going).

Here is my DIY set up ( post#15 ) :
http://www.aquaticplantcentral.com/forumapc/aquascaping/51836-davemonkey-s-50-gal-journal-2.html

I use 1-gallon orangejuice jugs since I have a larger tank and I double the recipe in them. I just punched a nail through like grim is saying and pulled the tubing through. If it is 'too easy' and you think the hole may be too big, you can seal with some aquatic sealant, but that will degrade over time.

It usually takes a few hours for fresh sugar/yeast to build up pressure and send CO2 through the tube.

-Dave

EDIT: I forgot to mention. I tried using a 2 liter bottle once and the cap was very hard. When I poked the hole with the nail, there was a VERY TINY crack beside the hole. It was enough leak out all the CO2 pressure, so maybe that has happened to you?

 

[davemonkey]

so is the diffuser a waste then??

No. It will work if you have more CO2 being pushed through the tubing (add another bottle of DIY, or use more yeast to increase CO2 production...but the sugar will be used up sooner) . Keep in mind, though, that you will need a "filter" bottle or a bubble counter in-line to catch all the DIY "snot" so that it does not clog the diffuser.

Even if you decide to go without the diffuser for your DIY, hang on to it in case you switch to pressurized one day. Or you could sell it.