They can provide an effective charcoal filter - removing all impurities as messages pass up the line.

The undergarments are air-tight and provide a pocketed escape hole in which a charcoal filter can be inserted.

As expected, much of the advertising, particularly that in print, centered on the charcoal filter and its effect on taste.

The discharge from the filter and the washings are run into a vat, and from this they are allowed to pass slowly through a tap into a charcoal filter.

This system often consists of activated charcoal filters that remove radioactive isotopes from the air.