The cheap way is to use an empty plastic 2 liter bottle, Fill 1/8 of the bottle with sugar, fill 1/3 of the bottle with Luke warm water and shake to dissolve the sugar, After this pierce the cap with a pin...Now one non-heaped table spoon of yeast close lid and shake, Then just leave in your grow room under a fan....Don't Over Do It With Yeast You Have Been Warned...I did this mistake myself by putting too much yeast and each bottle sprayed yeast on the sides of my tents smelt like a brewery...I'd let the 1st reaction occur outside of the tent to be safe..after this put in your grow tent and re-shake everyday to slow release Co2...