INJURED WAS WORKING INT HE COUNTER TRACTOR IN THE SECONDARY BASEMENT BY THE SOUTH END OF THE SECONDARY MILL #4. EMPLOYEE WAS UNPLUGGING TH EDISCHARGE DRAIN PIPE ON THE SECONDARY MILL DISCHARG E SUP ON SECONDARY MILL #4. WHEN PIPE UNPLUGGED EMPLOYEE WAS HIT BY THE WATER AND SLURRY AND EMPLOYEE WAS BLOWN BACK INTO A WATER PIPE.