"Das ist die Toilette?"
I don't think so in English if you were asking someone where the toilet was you would say "is that" not "that is" so DL won't allow it because it's not something we'd actually say
Read that wrong turns out DL is being pedantic and won't accept a more grammatically correct answer
Yep. We're taught that we start off a question with "is that..." but in conversation, you will hear people say "that is..."and end with an upwards inflection so you know they meant it as a question. You can even hear the inflection on this example, so you know it's a question, not a statement.
There is something right and wrong to what you are saying - In general, when asking a question, e.g. to find the toilet, you would ask "Is that the toilet?" - "Ist das die Toilette?"
But when in a different situation, you may use the other question. For example, when somebody tells you "This is the toilet!" and it's in a place where you wouldn't have expected it to be, or you are totally in disbelief because it does not look like toilet to you, you would reply with the question "This is the toilet?" - "Das ist die Toilette?"
So you can't interchange them as you please, same as in English.