I’ve not cleaned any of the newest ones with the clean outs on the side (though I doubt they help a ton).
typically for wax it takes a combination attack. The bulk of the work needs to be done power washing up directly through the holes, best while it is running (you can just run water). I’ve also removed the foamers and put a water hose through that point to get more water/pressure flowing.
Tends to be messy but all does the trick. I recommend making it a maintenance item as it is a lot easier if you do it periodically