Sludge

  Sludge is a buildup of degraded fuel that will clog fuel pumps and fuel injectors.

 
 
Actual bulk 200 million gal storage tank, drained and being cleaned of sludge.   In excess of
18" of sludge was removed (57 truck loads in total.) 
 
 
 
Photo reveling contract between sludge built up and a small area scraped clear.