Dirt is found in houses very often and is able to be cleaned with the Clean Tool. Dirt is found in many forms, including graffiti, spills, and stains. It can often be not very visible which is one of the main purposes of the mini map, which allows you to see dirt on the map. Buyer responses can also indicate if you have cleaned all of the dirt in the house, though this is somewhat unreliable. In order to clean it, you will need to hold down the left mouse button (PC only). Cleaning a house can be quite quick as long as you have fully maxed out the perks for cleaning, and continually run the mop around the house without stopping.