The "tunnel shower" was a design to quickly shower down large numbers of PE students yet not require large amounts of locker room space. The exiting line of students provided an efficient system to take shower attendance and towel issuance.
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Many schools emphasized cleanliness for all students before entering the swimming pool. Several authors have described their experience as freshmen entering the pool for their required PE swimming class. A soap shower, a walk through foot trays containing disinfectant solution, then a march through this "under carriage spray" assured that they would pass hygiene inspection prior to participating in the nude swimming class activity.