In high dirt-plus-grease situations, I have sometimes brought along a 5-gallon pail and a bucket heater. Drop a terry cloth pad into the bucket of boiling water, or a water-detergent solution, then - using tongs - pull it out soaking wet, quickly place it onto the soiled carpet, then get your OP machine on it real fast so that you can scrub before the heat in the pad dissipates. This has worked best for me when using the 2-sided, 100% cotton Argo pads, probably because their relative thickness holds more heat longer than thinner pads.