Most stains that are allowed to dry overnight will become more difficult to remove. This also applies to hot tea and especially coffee, as they become heat set.
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Attach the TurboJet negative air machine to the system. It can be attached to a Floor Duct or the Furnace Plenum with an Adapter Plate. The Pogo Pole Hose Adapter can be used to connect to ceiling and wall ducts.

The Cobra Power Brush will aggressively remove duct debris.

The Sidewinder Air Powered tool will remove duct debris more gently.

Decontaminate cleaned ducts with Sporicidin, Soot set sealant, and Odor Kill Deodorizer.