Mechanic - BU needs help from PU at 1st

[newump]

no runners on. ground ball to F6. throw pulls F3 off of the bag. he attempts a swipe tag of the BR. BU does not think he got a good look at the tag attempt. how should he go about asking for help? should he ask for help prior to making any call ? ie. BU makes no call and immediately points at PU and asks "do you have a tag?"
same thing for a pulled foot?
i've gotten some differing opinions.
i was also told by a veteran D1 umpire that BU should never ask for help on a pulled foot. only a swipe tag if necessary. i believe he is wrong and asking for help on either is acceptable. i know that BU should do his best to read a bad throw and attempt to adjust his position to get a better look at a tag or pulled foot situation, but i was under the impression that it is acceptable to ask for help in either of these situations.
thoughts? thanks.