Mud plug

a plug for stopping the mudhole of a boiler.

See also: Mud

Webster's Revised Unabridged Dictionary, published 1913 by G. & C. Merriam Co.
References in periodicals archive ?
After the hole is cut, a mud plug or pig is pulled through to clean the hole.
ANGRY Cliftonville skipper Mickey Donnelly threatened to retire after suffering red-card agony during the Smirnoff Premiership mud plug against neighbours Crusaders at Solitude.\ Donnelly's dismissal, in the 54th minute along with Crues hotshot Crawford McRae, means the veteran must sit out Saturday's Irish Cup quarter- final against Carrick Rangers at Taylor's Avenue.