I have been using the same gray 44 gallon garbage can for over a year and have never cleaned it out. It is always full of water, I have a 90g tank and do 15g changes weekly. The same day I change water I replace what I take out. If I HAD to clean the container everytime I changed water that would be a major PITA! There is residue on the inside of the gbc, my water tests fine so I'm not worried. I'd rather watch my fish zip around in the tank.