Related Clues:

• Underground TV
• Test this for difficult multiplication?
• Railway system, however, running west to east
• Something found after test in the London Underground
• Bank, say, most efficient at breaking out in depravity
• Pipe - Underground?
• Long, hollow cylinder
• Underground - cylinder
• Pipe (with trains?)
• Pipe - railway
• The idiot box
• Underground transport
• Rabbit ears sporter, once
• Poster mailer's need
• Drum engineer out from cylinder