The most common and most likely answer to this crossword clue is the 6 letter word SUDSER
S
U
D
S
E
R
More clues leading to the result SUDSER
Buddy explains!

The straight part
We know that "Dallas, say" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case dallas, say = sudser.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does SUDSER mean?
SUDSER noun- A foaming agent used in detergents etc.
- (entertainment industry) A soap opera.