Sentence-Usage : "How long has this been empty for?" Or "How long was this empty for?"

Question

I'm asking this because I have a feeling that if I say How long has this been empty for? , It would be like an ongoing action. For example:

A: How long has the dog's bowl been empty for?

For about an hour (it's still empty).

But, I feel that it's "grammatically wrong" if I Say How long was this empty for? without having a time expression. But, if I say using the present perfect, it'll be an ongoing action (And I don't want this). I want to say this:

A: Fills the dog's bowl with food

A: How long this has been/was empty for?

B: For about one hour.

but if I use the past simple, I think it will be wrong.

Answer 1

But, I feel that it's "grammatically wrong" if I Say How long was this empty for? without having a time expression.

There is nothing wrong here with the grammar.

The choice of the tense depends on context.

If you are asking that question, to your friend, pointing at the empty bowl, then it should be

How long has the bowl been empty for? [It is still empty at the time of asking the question]

If you are in the act of filling the bowl up or have already filled up, then you say

How long was this empty for? [The bowl is not empty anymore; you have filled it or, you are filling it]

Compare the following:

How long have you two been married for? [Still happily married]

How long were you two married for? [Still happily married]