I use 2L and 3L bottle, with rubber stoppers from a science surplus store. The rubber stoppers come with a hole through the middle and i just insert std. airline tubing in and everything fits tightly so theres no need to use anything to seal.
i have been trying a one gallon hawiian punch bottle for mine. I figured it would be a good volume and i filled it just to the part where it started to slope in hoping that having a larger surface area would allow for faster out put into my tank.
So far so good, been having a few leaking problems in my bubble counting crap collector so i took it outa the loop again to test the reactor that i finished building with left overs from buying another 120 this week.
I think i'll stick with this bottle until i can come across something better i have two puppies and a two liter would be a bomb for them to play with i dont want a mess like that.