By regular soap, I hope you mean regular soaps or detergents for pressure washing these are very often quite similar to foam cannon soaps. Though they aren’t entirely equal. While you can use regular soap (as long as it’s designed for pressure washing) instead of a foam cannon soap. You should double-check before you put a foam cannon soap into the detergent tank of your pressure washer. This is because the soap will often travel through your pressure washer pump, which can get damaged if you aren’t using the right soap formula, one that’s designed to go through the pump together with water. Since a foam cannon is mounted to the very end of your pressure washer wand, there is no issue with using regular soap for a power washer being used in a foam cannon soap bottle.