So I'm still confused. The "cap" (often has a "child safety" feature). You tried using tweezers on that (or the spout cap under the main cap) Please explain. Main cap requires squeezing and/or pushing down at the same time (especially the first time) The spout cap requires something like a butter knife (and still there is a trick to doing this... much better off with the tool suggested)
Either way, tweezers are useless. I'm a mechanic and have many tools (I understand most people don't have many tools) I'm not sure if any of understand exactly what you are trying to do. Did you manage so use the 30 ml anyway (and estimate how much nic shot to add)?