I had this nasty brown stain in my washer and I tried almost everything to remove it without even making a dent. Then I remembered the product called CLR (Calcium, Lime and Rust). I used this by wetting a sponge and simply letting it soak on the stain for about 4 minutes at most. This stuff came right off!
These stains really come from iron in the water and letting the wet clothes sit too long in the washer after the cycle has stopped. So having your water tested and or installing a whole house water filter may be a good idea. Home Depot, in most areas, will do water tests in the store about once a month.
The small bottle of CLR shown in the video was bought from Home Depot for about $5.50.
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