cheap toilet bowl acid will clean it.Make sure its hydro. acid leave on 30 seconds and rinse.I use one gallon vinegar to flush system when thermostat is removed.Heater on drive for 30 minutes.Then rinse till smell is gone.Better than citric acid.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran, deutschland deutschland uber alles uber alles in der welt