Vacuum first and pre-treat tough stains. 1 tank-full cleaned a 12' x 12' (3m x3m) carpet that was vacuumed routinely, no shoes on carpet but not shampooed in 15 years. Waste water was brown. Will redo high traffic area in a few months. It's heavy, pulls about 1.25 gallons waste water out for about 1.75 gallons solution used. Vacuum well first as it pulls up all the hair and dust. I said it twice, but don't forget. It's not a miracle worker, but I really like it as it works well, though it's a beast to push back and forth. I also clean the debris filter where the waste water tank connects to the vacuum manifold (?green color?) by vacuuming and brushing with a tooth brush. Mine was 25% filled with debris at 4 uses.
I have the bissell big green. Best carpet cleaner i have ever owned. But 1 saml correction. You shoudl not out solution kn the big green. For cleaner carpets put the soltuiton in a 1 gallon pumpsprayer. After you vaccum use the pump sprayer to spray the carpet then use a regualar push broom to agitate the solution in the carpet then use the big green like the video says 1 push foward and back with the trigger pressed then one pass forward and back with it released. Carpet came out much cleaner and cleaning the big green after wards was much quicker too.