The front tire of my heavy bike had a slow puncture. Slow, but not slow enough to ignore. It needed reinflating every day.
So I turned it upside down, undid the nuts and pulled the wheel partially out. Partially, because it's wired in. I took the tyre off, and pulled the inner tube out. I noticed that it already had a patch, and when I submerged the tube, the bubbles were coming out of the patch.
I'm rubbish at patching inner tubes.
So I replaced it with one of my thick-walled inner tubes. In my experience, those just don't get punctures.
It was a huge struggle to get it in place; the thick-walled tubes are a lot harder to manipulate, but I think it's worth it. After much effort, I got it on, and after more much effort I got the tire back on. I've inflated it to 45 psi, and I've left it, to see if it's OK before I put the bike back the right way up.