Investigate machines offering a good vacuum lift (not to mention air flow rate) in order to effectively extract much of the solution pumped into the carpet , therefore leaving it substantially dry. In fact, spend a little time researching this site. Prochem, Extracta, Ashbys and other popular machine manufacturers always specify the "Water Lift" in inches to guide you here. Watch the weight of the machine however, some machines are very heavy (bad back!!). Also, do book onto a Training Course where the instructors will guide you through the various processes and discuss the common problems.
Regards
Pete (JS2)