滔 is primarily a bound form that appears in compounds: 滔滔 (torrential; voluble), 滔天 (overwhelming, sky-high - said of waves, crimes, anger), 滔滔不绝 (to talk endlessly). It rarely stands alone.
氵 is the left-side form of 水 (water). 滔 describes water that overflows, surges and crashes - torrential flood-water on a grand scale. Most famous in 滔滔不绝 (talking non-stop, literally water-surging without break). The radical is essential to the image.
舀 (yǎo) supplies the sound, drifted to tāo. 舀 itself shows a hand reaching into a mortar 臼 - the act of scooping. The watery surge of 滔 leans on this for sound, though one can read it as water needing a giant hand to scoop. Same phonetic: 稻, 蹈。
