Ah. As I suspected.
.......
May I suggest you check the SLANG section and carefully read through it for the less 'politically correct' version of "extracting the urine", and maybe you'll see what I meant in jest!!
To answer / quote you: "2. Empty vessel sounds much." A favourite of school teachers everywhere!
Corrected to: "An empty vessel (pot / jar) makes the most noise"
Banging an empty vessel makes a lot more noise, compared to a full one.
ie. The less knowlegde you have in your 'vessel' (HEAD. If empty headed - a person who has 'nothing between their ears', or with no knowledge) the more noise (useless speech) comes out of your mouth.
Now am I 'extracting the urine'.....or not?
..or should that be 'Taking....the.....