I know this does not directly answer your question but it may help with your water extraction cleaning. I used to manufacture commercial carpet and the most common problem I saw with regard to cleaning was soaps that were not rinsed off and caused an accumulation on the fibers. I suggest that every third time you do a cleaning, you use just hot water. Always get the water as hot as possible. The term "steam cleaning" is used but it is really hot water and not steam, in the home cleaning units that Hoover and others make. When soap accumulates on fiber it attracts and holds soil. So sometimes soap can make the carpet dirtier quicker. Rinse well and vacuum as much of the water as possible. Good Luck.