I previously used those squeeze bottles but they're a pain to clean and sanitize, as I tend to have syrups in them for two months at a time and like to make it last.

I now use mason jars with flip caps: https://smile.amazon.com/gp/product/B07FB4HHLW/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&psc=1

The pour can be messier but still less so than pouring any spirit, sometimes a drop hangs out on the rim. I don't mind though because I can just put the jar and lid in the dishwasher now, so much easier.