I use this product formulated by a former washer repair guy. It's been around for more than 10 years, and it sold at Ace Hardware stores, and a variety of other places plus on line. You use just a small amount regularly, and it seems to help with build up.
I just bought a new front loader, and was told by the guy who installed (who also repairs washers) that he recommends using powdered detergent to help reduce build up and smell. He claimed that there's a small amount of fat/oil (can't remember why it supposed to be in there) in the liquid detergents and that's what makes it congeal on the surfaces around the outside of the tub and then start to smell. I'd guess that liquid fabric softeners contribute a lot, too.
With my previous washer, I had used powder for years and then as it became harder to find at my local store, I'd gone to liquid. And for the first time I started to have order problems. The Smelly Washer stuff cleared it up. Now with my new washer, I've started using the Costco powder and it seems to clean fine. We'll see if it helps hold down the build up. My new washer has a special "deep clean" cycle you run every so often to clean the area surrounding the tub.