WAS IN BASEMENT OF COLORING DEPT TO FIX ELEVATOR. BASEMENT WAS FLOODED WITH SLURRY AND WHILE WADING THRU SLIPPED OFF SMALL UNSEEN LEDGE AND FELT KNEE GIVE. MILD TO MODERATE PAIN, NEGATIVE FOR ANTALGIC GAIT. DID NO RESOLVE WITH FIRST AID MEASURES. DX OF RIGHT KNEE STRAIN.