teflon spray the Oring and wipe it off, or a bit of nose grease works too. I have 6 of these and not one of them leaks. I press down in center of the lid and have caps loose/off so air can escape, then do the squeeze when tightening the caps after filling. I use 475-500ml but I am only doing one sheet so only have one holder in the tank so get some space from that. my only complaint is that the caps break easy if dropped on concrete, but they are a standard size and I have found alternatives, especially from PhotoFormulary plastic bottles.