You start off with a wet sponge + car shampoo or something like that. Then, in an upwards and downwards motion, start cleaning the seat until it is clean. Then rinse the seat off with municipal water. Allow to dry in the hot African sun for 1 hour.
Ya I just wash mine with the same car shampoo I use on the bike. It's been perfect.
I spray the dirty bits of the bike with my own degreaser product (similar to prepsol)...like the wheels, lower parts of the motor, bashplate, chain and guides etc. Then use normal Carwash without wax on the rest of the bike.