A screw on cap for a PE bottle (https://www.amazon.de/-/en/gp/product/B07TKL6V7L) with a hole for a 3mm hose (https://shop.schlauchland.de/silikon/schlaeuche/351/unterdruckschlauch-meterware/id-waehlbar/viele-farben?number=SU_V100_3mm_transparent).
This cap can be used to build a liquid supply for various applications. One (NSFW) is described here: https://pervertabl.es/milk-receivers-and-a-coffee-can-part-3