Don’t use hot water. Put about a 1.5- 2% solution (w/ your reg hw soap) on it, let dwell about 10min, and that Thompsons will wash right off with a low-medium pressure rinse. Try a small section to test first.
PS: Anyone with enough sense to get out of bed in the morning would know that a dark stain on a floor is going to show every bit of dust and dirt. Just so you’ll know the type of clients you’re dealing with.