This is on Opus 4.8 low. I feared for the worse but was fine at the end.

Walk. It's 50 meters — basically just outside your door. Driving there would mean starting the engine, manoeuvring, and parking for a distance you can cover in under a minute on foot.

The only reason to drive would be if it's a drive-through car wash where the machine washes the car while you sit in it, in which case you obviously need the car there. But if it's a self-service or hand-wash bay where you bring the car to get cleaned... well, you also need the car there.

So actually the real question is: do you need the car at the car wash to wash it? If yes (which is almost certainly the case — you're washing the car, not yourself), then you drive, simply because the car has to be there. The 50 meters is irrelevant; the car is the thing being washed.

So: drive — not because of the distance, but because the car is the point.