Possible Clues:

• Sounds as if Dorothy will be at the bottom of the pipe
• Portion that keeps dry - it's left in pipe
• Plug (especially of tobacco left in pipe)
• Tobacco remnants left in a pipe
• Plug of half-smoked tobacco
• At the end of the pipe, let it come at the end of the full stop
• Pipe residue
• Pipe-bowl residue
• Being left in the pipe it's got a 16 across
• Residue of tobacco left in a pipe