Kankens are extremely sturdy backpacks (my grandma’s had one for 10+ years) but cleaning them can be a finicky process (For the love of all that is sacred to you, do NOT throw it in the washing machine). If you have a light colored kanken or just need to remove a mark/stain, use a magic eraser. Wet a corner of the magic eraser and scrub as needed. Wet an entire side for larger areas. It’ll remove dye stains from denim jeans, dirt, charcoal, etc. After scrubbing, run it under lukewarm water in the shower to get the grime off and then air dry. I do this every few months or as needed and my peach kanken is practically spotless (and I’m an art major). Best of luck!