elbow grease

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun Strenuous physical labor and effort.

from The Century Dictionary.

• noun A colloquial or humorous expression for energetic hand-labor, as in rubbing, scouring, etc.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun idiomatic Effort or hard work, especially physical work involving repeated motion of the forearm, such as scrubbing.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun use of physical or mental energy; hard work