How to remove mildew stains from a tent?

I'd check carefully if the tent has any value.. Is it cotton fabric you have, probably but maybe not? Bleach is fairly strong stuff, probably kill the mildew alright but I could see the fabric possibly disintegrating at some stage, just when you want it to keep the weather out!!

If you do come to terms with it, prevention is better than cure. Try and take down a cotton tent (any tent) when there's a bit of a breeze blowing and it's dry as can be. Then air it in a shed or on a washing line when you get back. Store loosely folded, not stuffed in tight roll etc. Trust this helps