infection control questions

O.k. I have a couple questions .......beleive it or not I am not a
new nurse but am a little confused about some of our facility policies
regarding clean/sterile fields. Why can we reuse a non sterile cannula
for trach suctioning? What is the purpose for keeping a sterile field if we are
just going to stick a cannula that has been floating around their room?
Same with a s/p cath flush? We set it up to do a sterile flush then use
regular gloves and only alcohol the end of the bag and cath. Am I just being dumb here?