The answer to 'dryer vent stain removal' is that the most common cause of dryer vent stains is lint buildup. Over time, lint can accumulate in the vent and cause discoloration and staining on the exterior of the vent. Symptoms include visible lint or debris around the vent opening, reduced airflow from the dryer, and increased drying times.
For minor stains, you can often remove them by brushing or vacuuming the vent exterior and using a mild detergent or vinegar solution to scrub the stain. However, if the vent is severely clogged or the stains are persistent, it's best to call a professional dryer vent cleaning service to thoroughly clean and inspect the entire vent system.