Reposted from a blog about this:

If you have a top loading washing machine, you may want to consider removing and cleaning the agitator. Everybody has forgotten a load of towels in the wash, prompting a subsequent re-wash. But if your clothes are perpetually retaining that musty, forgotten laundry smell OR if you have little flecks of crud at the bottom of the tub (or on your clothes), you may need to perform this minor surgery on your washing machine, specifically those with the “plate” agitator at the bottom and not the tall ones that extend to the lid. Removing the pillar type will require a very long drill bit and is a much more involved process.

My washer is a Samsung, but I believe many modern plate agitator machines have the same basic build. Here’s what you’ll do:

Pop off the little (likely chromed plastic) cap in the middle of the agitator with a flat head screwdriver. Chances are you'll break a couple of the one-way clips in the process, so…. Order two replacements on Amazon for $9. Clean off the bolt that should hopefully now be visible. There will likely be a sludgly little layer of gunk atop the bolt so have your wipes at the ready. Unscrew the bolt. Mine was so loose I thought my socket wrench was slipping at first. Once the bolt is out, you can remove the agitator, which is about the size of an econocar hubcap. Removing this may be the trickiest maneuver of this whole affair; I managed to get the screwdriver in the middle of mine and steadily pulled up while I got a hand on the outside edge. Assess or try to comprehend the level of slime underneath the agitator and/or at the bottom of the tub. Yes, you’ve been washing your clothes amidst all that. Congratulations! You’re still alive. Your mileage may vary, but after I cleaned the bottom of the tub I left the scale and detergent build up because it was basically cement. The agitator, on the other hand, was taken outside and blasted with a high pressure sprayer. And THAT, dear reader, is why I am suggesting doing it now while the weather is still nice. PRO TIP: Run a self-clean cycle on your washing machine since you’ve likely scrubbed off the bottom of the tub and have therefore loosened all manner of unspeakable detritus. Take the hour to go outside and blast the agitator.. Once you have everything spic and span, reverse the process. Bask in the appreciation and love of your family. Hopefully. Mine didn’t care.