I think ''with salt'' means that he use additional salt
Because we use salt when we cook soup,so all of them are salty
I am not sure though
"Bazen tuzlu çorba içer." Translation: He sometimes drinks soup with salt.
As you can see from my answers he/she & it are accepted.
These are the clues in the adjective & verb:
Tuzlu - (adjective) - "with salt." Tuz - "salt" + (l) buffer + "-u" possessive case back vowel suffix.
İçer - "drinks." İç - "drink" + "er" suffix for "drinks."
Always look for possessive case markers in such Turkish questions.