I'm installing a 120 volt, 20 amp circuit with a 20 amp receptacle for a sewage pump for a septic tank outdoors.I have a 4x4 post where I mounted a weather tight box with a single receptacle with an in-use weather tight cover.The pump plugs into the receptacle and has a piggy back plug which is a float switch.Does this circuit have to be GFCI protected? I need to know the code article.Thanks