Drain blockage is a common plumbing issue caused by the accumulation of debris in the pipes. The two crossword solutions for this term are CLOG and CLO, both of which refer to an obstruction in the pipe that prevents water from flowing freely. Clogs are usually caused by the buildup of hair, grease, soap scum, and other materials, while CLO stands for Calcium Lime and Rust, which is a type of mineral deposit that can form in pipes over time.