Back in the "olden days" when dad wanted me to clean the mud out of his International pickup I'd take a bucket of water and toss it in, then scrub it with a horsehair brush. With rubber matting on the floor, vinyl seats and a metal dashboard it washed up quite nicely and was rinsed with a clean bucket of water. I usually did that 2-3 times each summer, usually on a Saturday morning so it would be clean for our weekly trip into town on Saturday afternoon and church on Sunday morning.
A lot of the water drained out from the boot around the gearshift, the rest cascaded out the doors. A few minutes with the scrub brush and rag and it was shiny and clean. Leave the doors open for a couple hours and it was dry and ready to go to town.