I try my best to run a cleaner or two through the pipe when I’m done smoking, and I often run one through before packing, but I’m also known to not care much and will forget. It’s also not wrong to use a cleaner during the smoke. I do a deep alcohol clean a few times a year on rainy days. I also water flush fairly regularly, but I’m not terribly religious about keeping my pipes clean and spotless and I don’t feel like my enjoyment suffers any. If a pipe gets nasty (my cobs can be pretty foul) I’ll certainly address it, but day to day I take a relaxed approach.
I used to be much more careful about it, as I believed the dogma that if a pipe has one iota of tar left over from a previous smoke, I was somehow doing it all wrong and not smoking to my full potential and thus wouldn’t pick up on those nuances of toast and maraschino Cherry skins or whatever the hell I was supposed to taste, but I’ve come to the conclusion that whatever works for each of us is just fine.