There is a drain plug on the rear of the lower oil pan. The size is 13mm and when removing, if it does not come out after loosening with your fingers, replace due to being over torqued.
Keep in mind the best method of draining the oil is via oil suction, actually removes more oil that draining and less mess. There are several aftermarket oil vacuum devices available.
Mercedes-Benz Master Guild - 2 years
Shop Foreman - 20 + years - dealer.
Part owner - MBZ Transmission remanufacture