I wrote this review to explore how sleep helps the brain clear out waste and why this process might be important for aging, memory loss prevention and brain diseases like Alzheimer’s. The brain has a cleaning system, called the glymphatic system, that works like a cleaning network during sleep. While many researchers have studied different parts of it, few papers bring together findings from brain anatomy, sleep patterns, aging and genetics all in one place. My goal was to give a full picture of how sleep supports brain health and what might happen when this system does not work properly. I also pointed out where the science is still unclear, what questions remain and how future research could improve our understanding. By reviewing the strongest ideas in the field and suggesting possible ways to improve brain waste clearance, I hope this paper helps move the science forward.