I do mine about once a month in the summer, once ever time it warms up in the winter and the outside gets washed just after the spring thaw and several times in the summer and fall... i'm a clean freak
People sometimes leave candy wrappers or empty soda cans in my pannier bags when my bike's parked outside the supermarket (last week somebody put a huge bag of old bread in there, what was up with that ?), I always deposit those in a nearby trashcan right away.
I will normally wash it once or twice in 3 years of owning it. That's the fun of having agray car.
As for internal cleaning. Heh hehe...ummm...way less then I want to. However I always feel better when I get into B's car. He uses his backseat as the garbage can
I try to keep my car clean- well, I try to keep my NEW car clean. I just washed it at the carwash last weekend and cleaned out the inside (including vacuuming). Since I just got it in July, I washed it a lot during the summer. My other cars usually went years at a time before I would clean them
My white Honda doesn't really show the dirt much, so consequently, it doesn't get washed as often as it should...maybe 4 times a year, and always at the car wash. The inside gets cleaned a little more often, but not much! Right now, the windows need to be washed on the inside, but it's so cold that I keep putting it off. It'll probably happen in the spring, lol!
We try to take good care of ours. I empty out all trash/wrappers/etc from the side doors at the end of every day normally. We wash ours every few months (maybe 2-3 months) or more if they need it and we keep rain x on the windshields/etc.
Well doing landscaping for a living does not help towards having a clean truck!! I can haul anything from plants (in the cab and the bed), screenings, pavers, topsoil, mulch, weeds, brush in the back.
One advantage of owning lots of land is I can drive and dump some of the debris on the compost pile, brush pile to be chipped up pile or burn pile!! I also have spots to park the truck on an incline and hose out the truck bed. But the exterior can get a bit grimey!!
The inside gets cleaned/vaccuumed out fairly often when I am in season working.
Its not too bad now that I'm done and the only items we will be hauling is firewood from the farm or lumber.
The car is much cleaner-except if I use it to buy/transport plants-then I have to vaccuum-thank goodness for leather seats!!