I use the syringe that comes with inkjet refillable bottles of ink. Back when I used to refill my ink jet printers, I would buy a package that had a black and the three color inks in bottles and came with a syringe. Well, over the years I amassed many many of these syringes (unused) and stuck them into a container thinking I might be able to use them for something else one day. The syringes by the way don't have a pointed tip, they're more flat which makes me feel safer when I use them.
So, when ever I need it like for the RSST tank I pull out one of these syringes and it fits perfectly into the fill hole while leaving enough space around it so that the juice doesn't come flooding out the top of my SS mesh wick. First time i tried it with the regular squeeze bottle of juice and I had a lap of juice before I knew it as it was ...... straight out the top of the SS mesh wick as the bottle nozzle blocked any way for the air to escape out of the tank other than the SS mesh wick.