Pour about a gallon of water into a bucket. Add 1/2 cup of liquid disinfectant or non-detergent soap.
Dip a sponge into the solution and wipe down the material of your tent. Sponge gently over the entire surface, particularly over any areas where you see mildew or fungal growth. Do not rinse or wipe off the tent after you've sponged it.
Locate an area outside that is warm but away from direct sunlight. Sun can break down the waterproof coating on your tent, which may already be weakened by the presence of mildew.
Set up or hang the tent in the shaded location and leave it outside until it has dried completely.
Wash the tent by sponging it down with a mixture made of 1 gallon of water and 1/2 cup of liquid disinfectant.
Add 1 gallon of hot water to a clean bucket. Mix in 1 cup salt and 1 cup lemon juice, or lemon juice concentrate from a bottle.
Dip a sponge into the lemon and salt mixture and rub it over the visible mildew. This will remove the mildew. However, stains that are left behind will not be removable.
Take the tent outside and set it up in the sun. Because the coating has already begun to peel, the sun will not do further significant damage. Allow it to dry thoroughly..
Apply a waterproof coating to the surface of your tent after it has had time to dry. Follow the manufacturers instructions for application.