Last Wednesday's reentry of the space shuttle Discovery included a purging of the human waste stored since docking at the STS-218, where flushing has since been prohibited due to sensitive environmental concerns of waste exposure to experiments connected to the space lab, the Kibo module. A failed earlier attempt to rid the sewage mass coupled with new restrictions produced larger than normal amounts than during other dockings. And it seems when the shuttle dumps, people notice. Since any water molecules quickly freeze into ice, the sun can reflect its form and illuminate for observers to see.
http://www.space.com/missionlaunches/090911-space-water-dump.html