How often should i clean my rats out?

i used to use paper based cat litter in the bottom of my rats cage, and i would clean them out 2 times a week. well i decided to buy them some dog fleece blankets, they have 1 in the bottom of their cage and 1 at the top. but im not sure how often i should wash them. the have mixed rat food, so they end up taking parts of it to different areas of the cage, and the small bits of grain get stuck on the blanket, and its hard to get them all off. btw i cant buy them lab blocks. the place that sells them is too far away from where i live, and my dad works alot, so he cant take me. so i want to know how often i should clean the blankets. everyday or say every 3 days.