You will have to re-waterproof the tent, so go to your local outdoor equipment place to get either wash-in or spray-on waterproof.
Of course, the best thing is to not have this in the first place. Always set up your tent when you get home to check for damp, tears, pine pitch spots, dirt, etc. Repair or clean, and THEN roll it up and put it away for the next trip.
Source: 40+ years of Girl Scouts, plus 9 years of Boy Scouts.
By Eileen from Elk Grove, CA