How do you clean a backpack?

I keep a pack strapped on my bike rack, so it gets fairly dirty. I've been brushing/vacuuming it, but I'd really like to use soap and water. The last time I used regular detergent on a backpack, the inner lining started to peel away so I'm not going to do that again.

I've seen some websites that say use "mild soap" -- but what is that exactly? I have "delicate wash" from Ecover.

Any ideas/suggestions?

Soap and detergent are different, chemically, so read the label. I use pump hand soap or a sudsed-up bar of Ivory when mild soap is called for.