Air in engine - burping

Seasons greetings & I plan to be flying on solstice   : } 

So I see yet another thread on burping, ha if it werent for burping & sinking floats ... this foro would wilt !  j/k

It is amazingly difficult tho., to figure out how to post a post, i have just the nondescript grey button way up & away from the threads ... 

Anyway, many of us were under the impression that burping was requiered to clear the engine of oil & air for the first few compression strokes ... not true, ive learned here   ... but this air in the engine scenario needs a stand alone thread.  Ive learned reversing the prop is a big no no,  I think ive read here that we should not hand prop the last of the oil w/ the oil filter off. I think ive read here that the oil cooler should not be drained during a oil chng.  In my installation, the oil cooler is well above the oil tank, so i assume it drains.  I think ive learned any suction of air into the engine is not good & will require a "purge". 

Well what about the suction occuring during compression testing or finding top dead center ?

With the oil system open to the environment via the overflow line, isnt the inside of the engine equal to the external pressure ?

Hopefuly one of our gurus will take time to educate some of us.

Heres hoping 21 is much better than this, one of the worlds worst years in modern times.  I'm greatful my own life was buffered for the many impacts, hope yours were too ...i'll leave w a view down @ phx sky harbour ;1'st time ive flown in class b,  not gonna try that again  :p

Roger, when this damnvirus abates, i hope you hold another basic class, clearly i need it!