After watching the video on DIY professional grout cleaning, I'm not going to even try and delve into the inaccurate tittle here, I wanted to correct some information in the video. Most professional grout cleaners in Tampa FL use a high alkaline cleaner to break down grease and emulsify soils, but they do not use an acid rinse. Rinsing with water works just fine. Acidic solutions can damage metal surfaces like stainless steel on your refrigerator, dishwasher, and stove. If you decide to use an acidic solution for "professional" grout cleaning be careful not to get it on your appliances. I would highly recommend taping off your appliances before cleaning to make sure they don't get damaged.
Professional grout cleaners do use acidic solutions from time to time to etch grout, removing the top layer of grout that is stained or discolored. Acidic solutions are terrible cleaners in general and shouldn't be used for grout cleaning.
As a professional grout and tile cleaner in Tampa FL I do not ever recommend pouring your chemical laden waste water out in your yard. It can only harm your ground water and contaminate run offs.