I've been using a syringe and 18g or 20g needle. Syringe size, I'd say don't go bigger than 12 ml (cc) or it'll be too hard to push thick liquid through. I use the 1 1/2 inch needles (we use them for sq fluids or cysto's on the animals (I'm a vet tech). I usually put the needle in the mouth side on an angle into the stuffing and push .75 ml's in. Then either Taryn's spin method or shake them down like a thermometer. I leave the .... plug and condom on the battery side. The 20g needle will go into the bottle without removing the dropper top...18g is a tight squeeze but it's faster to draw it up with that. Takes me literally 2 minutes to refill 10 carts.
You can order just a few of each or syringe with needle attached from a few animal supply companies online. KV Vet is one and Jeffers is the other I order from when I have to (I usually just get them from my vet).
I'm lazy and can't be bothered taking off the plastic ends...besides, once I do take them off, they tend to pop off when I'm biting down on the cart...refilling like this avoids that and is the quickest most efficient way I've found so far. The best part is Taryn's spin method. Without that you get gurgling and juice in the mouth even letting them sit. I found that trying to get in 1ml on a refill is tough..guess it depends on how dry the cart is. I've never had a problem with .75ml's.
Happy refilling
