As a person who cleans cars full of spots and other *****, using really strong detergent is the only way. Wet-vac once youre done helps you make nice lines in the carpet so it looks freshly detailed. The carpet in MBs is nice enough that you can clean it as long as its not been wearing in for months.

Soaking it will help and let it dry before you put it back in the car otherwise it will start smelling like theres a dead rat in your car.
Peter