Do you clean your records before play, after play, or once (and then never again)?

I don't like using the stylus as a dredge, but even after cleaning, some old records will still sound distorted or churn up stuff or foul the stylus- I will do an intensive re-clean, but at a certain point, if the record isn't playing cleanly, I'll look for another copy. I did manage to revive some old copies by multiple cleanings using different cleaning methods, including ultrasonic, but my practices vary, depending on the condition of the record. Every once in a while I'll get an old record that is pristine, but that's the exception. 

Map- check out Rushton's thread on DIY US if you haven't-the price of entry isn't crazy, and you can arguably get better results, but it isn't about convenience. And in my estimation, you still need some sort of vacuum machine, to take advantage of different kinds of cleaning, which work synergistically.  

@bradf - you might look at Rushton’s thread here, which is based on an article he wrote for Positive Feedback. There is a relationship among size of bath, number and power of transducers, frequency, etc. viz surface area of records to be cleaned. (Sorry, I don’t remember the formula--it is buried in the long thread on DIY Audio about ultrasonic cleaning). @terry9 can speak to his experiments with the number of LPs in the bath v. cleaning effectiveness.
The bonus to DIY isn’t just cost-effectiveness either. You can take advantage of higher frequencies, heat control and other features that aren’t necessarily offered on the audiophile machines.