defile, blaspheme, ditch
涜 centers on polluting or desecrating something pure or sacred: defiling, blaspheming, or turning something into a dirty ditch.
涜 is the modern simplified form of 瀆. The older form combines 氵 (water) with 賣, which likely contributed the sound and the idea of a ditch or defilement. The modern 売 shape is a simplification.
Water 氵 beside 売 suggests a dirty ditch or a polluted channel. Picture water flowing through a filthy ditch, defiling everything it touches.
For トク, imagine a toad croaking in a defiled ditch: toad -> トク, and the toad's presence makes the water even more polluted.