i have a mate in the valeting game who has a car wash too, i get to use his gear and when it comes to carpets or mats its out with the tfr and then blast it clean with the diesel power washer, then chuck over anything in the sun to dry out.
you can see the crap come out with a proper blasting, just don't go too close or you can go through, you can just use a diy power washer but its not as effective as a big un.