Listen to pupilage , and use a soda bottle. If you are making a larger batch , then use a bigger container that is also made out of PETE. Stay away from HDPE. Imagine you are in the middle of shaking , only to have your newly made ketone eat thru your KRV and then splash all over your face. Eck. Remember you can only scale up the O2 to a certain amount(100 ml per run). If you get greedy , expect failure.