I think that there is a sense in which a B theorist will likely agree that tensed expressions (is / was / will / etc) are primitive and unanalysable. A B theorist will typically not hold that tensed expressions are elimimable from ordinary language, that they can be actually dispensed with.
I will quote hereafter from an online article by D.H. Mellor from Cambridge U, a B theorist, author of the book Real Time on the philosophy of time.
As far as truth is concerned, Mellor holds that tensed expressions are analysable, along the following lines:
It is the case = at the time of this utterance,
It was the case = before the time of this utterance,
It will be the case = after the time of this utterance.
An ability to demonstrate at an utterance is granted here, supposedly without involving, however, an antecedent reference to "the present time".
What then does make A-series statements true? Again the answer is simple. For example, for any X, statements of the forms 'It is now X', 'X was last week' and 'X is due tomorrow' are made true respectively by being said at X, in the week after X, and the day before X is due. But those are all B-series facts, about when things happen and are said, regardless of which if any of those things and sayings are present - which is why these B-series facts imply no contradiction.
Mellor also holds, however, that tensed expressions are not replaceable when it comes to self knowledge. Like other indexicals ('here', 'now') and demonstratives ('this', 'I', 'you'), tensed expressions encapsulate self awareness in a way that cannot be emulated by B expressions. When Joe says on Wednesday "it will rain tomorrow" it carries the same truth content as if he said "it will rain on Thursday". But if Joe happens e.g. not to know that today is Wednesday, the two phrases are not epistemologically equivalent.
That for example was what caused me to go to London on 22 October 1999 in order to give the lecture at the Royal Institute of Philosophy . . . I went there then because I wanted to give that lecture, which I believed I was due to give there on that day. But for that belief to cause this action of mine it had . . . to be both a personal and an A-series belief. Believing that Hugh Mellor was due to speak in London on 22 October would not have been enough. That belief did not after all make anyone else go to London to speak, simply because no one else believed 'I am Hugh Mellor'. Nor would that belief have made me go to London then if I had forgotten who I was, and thereby ceased to believe that the speaker was not only Hugh Mellor but me. And similarly with the date. Wanting to be at the lecture, and believing it to be on 22 October, would not have taken anyone there on 22 October unless and until they also acquired the A-series belief 'Today is 22 October'.