gourd
瓠 centers on a gourd, specifically a type of calabash or bottle gourd used as a container or vessel.
瓠 combines 夸 (likely a phonetic component) with 瓜 (gourd/melon), forming a character for a specific type of gourd. The exact historical development of 夸 in this context is uncertain.
The left side 夸 looks like a big 大 over a container, and the right side 瓜 is a gourd. Picture a large gourd being used as a bottle or dipper.
For コ, imagine a gourd shaped like a small 子 (こ, child) container: 子 -> コ, and the gourd holds water like a little child's cup.