Postmaster General John Potter said use of that particular type of cleaning machine has been discontinued.

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Rules govern how many hamburger patties to a pound of beef (10), how long to toast a bun (17 seconds) and how much sanitizer to use when cleaning the shake machine (1 packet for 2.5 gallons of water).

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Ms. McNally said her book machine occasionally jams, much like a copy machine, but her staff has become adept at maintaining it, by vacuuming and cleaning it with alcohol, so disruptions have become infrequent.

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