My question hails from a series of comments here in this answer.
Take a piss is a light verb construction in which the actual verb is take, but the noun piss carries the actual meaning. It corresponds to the heavy verb piss.
I did not get anything!
take a piss; take is not a verb with piss as its object, but "take a piss" functions together as a single verb. Thankfully, "I need to take a piss" is not grammatically the same as "I need to take an aspirin.
So, when we use
need to take a/an [x]
I surely consider that 'x' as a noun because it is following an article.
The comments by native speakers say that in such cases, 'x' does not serve as a noun because it is different. You don't take a piss but you take an aspirin.
Now, how to differentiate in such phrases whether that 'x' is not a noun?
take a look
take a piss
take a break
How to identify whether those 'nouns' don't function as 'nouns' though they are 'nouns!'