Been using the hard caps that are already on the tank for the first week of ownership and has worked perfectly. Replaced (for no good reason other than I realized they are not hard plastic, and thought I might be using the wrong cap) the hard cap on the tank this afternoon with the soft one that does not have a pre-punched hole, and notice there's leakage now. 
Question- Are the hard one's even supposed to be used initially (no leaks on either one I've been using makes me think so!)

Question- Are the hard one's even supposed to be used initially (no leaks on either one I've been using makes me think so!)