Subjective c/o generalized back pain after transferring 1/2-full 5-gal buckets ~3-4' from 3'H ledge to coworker; no lifting, stooping, or twisting required. Mandatory weekend shift; EE wanted to leave early, complaint is suspect. EE refused post-incident drug screen, admitted THC/marijuana use. Terminated for cause per zero-tolerance drug/alcohol policy.