@washerdude - There are two purge methods that I know of that Whirlpool machines use.
1. Prerinse purge - After the main wash, the machine fills with fresh water for about 10 seconds, then runs the main pump for a few seconds to agitate any remaining soils and detergent in the sump, then drains and proceeds to the rinse. For the PowerClean/UltraWash, the pump only turns on once for around 5 seconds, followed by a full drain. On Voyager machines, and the new resource-saver models (the Tahoe platform, from what I've found in WP service documents), the pump will cycle on and off for a few seconds at a time before draining. This clears the sump enough to usually only need one rinse afterwards.
2. Automatic filter purge - Whirlpool implemented this on the Voyager design, and if I'm correct, the new Tahoe design as well. This purge is done during the prewash and main wash portions of the cycle. As the machine pauses to test the turbidity of the water, it will decide whether a prewash is necessary or if it can proceed into the main wash without draining. It also decides if AFP's are necessary, and if so, the drain pump will kick on while the main pump is circulating water. This creates negative pressure in the filter chamber, and with the downward spray of the lower wash arm, the dirt particles are forced down and out the drain. The fill valve also kicks on for about ten seconds to replenish what was pulled out. This way, the accumulated soil can be removed without dumping the entire tub. The Tahoe works essentially the same way, pulling soil trapped in the manual filter out through the bottom.
My Maytag-Voyager will usually do two or three AFPs between the prewash and main wash if the load is of medium soil, usually skipping the drain and proceeding to dispense detergent, which in my opinion is the best method because the water isn't fully hot and is also soil-laden, so the enzymes in the detergent get a good workout and they're able to work well because the temp is gradually rising. I've only had it drain the prewash and fill for a separate MW a few times, and it was for a super nasty load. I've never had anything come out less than sparkling, and it cuts water usage down to maybe 3.5-4 gallons, and that's with all three arms running full force.
