to bale out water
戽 centers on the action of lifting or drawing water out of a container, like bailing out a boat or scooping liquid.
戽 combines 户 (door) and 斗 (a measuring ladle or dipper). The character likely depicts using a ladle-like tool to bail water out through an opening, though the exact historical development is uncertain.
Picture a door (户) with a dipper (斗) inside: you open the door and use the dipper to bail water out.
For コ, imagine a small boat with a hole, and you call out 'Co!' as you bail water: Co -> コ.