...since the bins have/had been emptied.

It's been six weeks since the bins have been emptied.
Where I live we would say this. Use of the present perfect is much more common in British English when we are (in the present) looking back at a time in the past when something happened and was completed.

It's six weeks since the bins were emptied.
American English has stopped caring so much about this, although the "death" of the present perfect in AmE has been exaggerated.

Thanks, contrex.

I'm somewhat puzzled by 'have' (present tense verb) in the first sentence and 'were' (past tense verb) in the second sentence.

It's been six weeks since the bins have been emptied.
It's six weeks since the bins were emptied.

But it would be wrong if I used 'had' in the first sentence:
It's been six weeks since the bins had been emptied.

Is my understanding correct? Thanks.

It has been/It's been six weeks since the bins were emptied.

It is (or it has been) six weeks since the bins have been emptied

If you use the simple past tense, since the bins were emptied, you are thinking at that moment of the last time the bins were emptied. If you use the present perfect tense, since the bins have been emptied, you are thinking of the gap in time since the emptying of the bins.

Thanks, contrex.

Your explanation reproduced below cleared my doubts.

If you use the simple past tense, since the bins were emptied, you are thinking at that moment of the last time the bins were emptied. If you use the present perfect tense, since the bins have been emptied, you are thinking of the gap in time since the emptying of the bins.

Betcha tho Con there's a subtle diff in meaning

Betcha tho Con there's a subtle diff in meaning

...but Tang forgive me, I'm not quite smart enuf