This video on upholstery cleaning shows you a really good way to clean your auto upholstery. Using a small wet dry shop vac is the key to cleaning success. I clean upholstery for a living in Tampa FL and I can tell you that towel cleaning will not remove all the soil in upholstery. You need to be able to extract soils with a vacuum. I'm not particularly thrilled with the dish soap cleaner that he has concocted for this video. Every time you add dish soap to water your adding loads of surfactants. These surfactants act as dirt attracting residues because they cannot be extracted without heavy rinsing. The soap will remain in the cloth fabric slowly collecting dirt and oils, slowly getting dirty. You can go ahead and use this DIY cleaning solution but you should rinse the upholstery with some clean water and extract the reaming cleaning solution.
I tell my Tampa FL customers to use carbonated water to clean their auto upholstery. You wont need to mix in any soap. Just spray it with carbonated water and then extract the soil. The carbonated water will lift the soil out of the upholstery and you wont need to rinse it afterwards. I've used it many times to clean out spills and messes in autos. If you have a soda stream or a bottle of tonic water you're all set. Happy cleaning.