flow
淌 centers on the movement of liquid: flowing or streaming. The meaning is straightforward and tied to water in motion.
淌 combines 氵 (water) with 尚, which likely contributes the sound. The exact historical development of 尚 in this character is uncertain, but the water radical clearly indicates a liquid-related meaning.
The left side is water 氵, and the right side 尚 looks like a small roof over an opening. Picture water flowing out from under a roof: 淌 means flow.
For トウ, imagine water flowing through a toe-shaped channel: toe -> トウ, and the stream flows along.
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