sack, bag opening at both ends
橐 centers on a container for carrying things: a sack or bag, especially one that can be opened at both ends for easy access.
橐 is a phono-semantic compound: the lower part 木 (tree) and 石 (stone) suggest a container made from natural materials, while the upper part likely contributed the sound. The exact historical development is uncertain.
Imagine a bag made from wood and stone: the 木 (tree) provides the frame, and 石 (stone) weights the bottom, with 冖 acting as a lid. This sack opens at both ends for easy loading.
For タク, picture a tack holding the sack closed: tack -> タク. When you remove the tack, the bag opens at both ends.