I like these: https://www.amazon.com/Ardes-Livestock-Vaccinators-Operation-Luer-Lock/dp/B01N24IHSM with small gauge blunt tip Luer Lock needles. I was inspired by TieDyeRon to try one out. They work great for precise work. It's especially nice to work from a concentrated dye and have some water handy to dilute down to different shades.