I got my wife these slim cart tanks with what they called a locking ring. Ok cool what ever. I get them in and do some youtube videso so figure out how to fill them and all. Ok so far everything is good. I am not sure if she really likes them cause i never see her use them. Ok again that is fine. I would like to get one for myself, but dont really want to spend a ton and i dont want a slim one. What i am lost on is the holes in them. I see places that selll the carts with pre punched holes. Some have one others have two and so on and so forth. Does this mean more liquid that can get it? I mean that makes sense for me. Also how do i know which carts to but to replace the ones that came in them. The ones in there seem to have a flange on them and it fits into these groves and then the locking ring goes on. My B & m's dont seem to carry carts so i am trying to do this on line. I do not like these slim ones cause it seems hard to fill them up. It was hard to get they syringe tip between the tank and cart itself. So any tips on carts to get to replace the ones she has plus a inexpensive larger capacity for me would be great. Thanks,