The trick to getting your car washed for free: loan it out to other people!
These days I'm not as consistent in washing my car as I would like. 10 years ago I would religiously take out the bucket and soap once every two weeks. Nowadays I thank the weather gods when it rains because that's a free car wash that I don't have to do. The key is to use wax when I do wash my BMW M2. The waxed surface repels dust and foreign debris quite readily, allowing the rain drops to do most of the work.
This is what happens when you get old, kids: you start caring less and less about keeping things in pristine condition. Not to say you should go the other end of the spectrum and actively neglect on maintenance. The goal is to maximize the utility for as long as possible. I certainly don't make the sort of money to be disposable with the expensive things I buy.
So that means I would have to wash the car every once in a while. There's only so much rain water can do, especially when California has been in drought conditions for the longest time. But recently I've noticed something: the last two times I let a fellow car enthusiast borrow the M2, it has returned to me freshly washed and fueled. That's the code: a gentlemen always return a borrowed car (or anything, really) in cleaner condition and a fully filled tank.
Obviously I try to also loan my car out in somewhat clean condition, and fill up on gas before handing the keys over. Courtesy begets courtesy. A free car wash, however, is something I can happily live with in this quid pro quo situation.
Spring time in the summer.