The most common and most likely answer to this crossword clue is the 8 letter word EMISSION
E
M
I
S
S
I
O
N
More clues leading to the result EMISSION
- Issue rebounding sound when phone card's installed
- Leak from European delegation
- Discharge key errand
- Primarily, ecologists’ crusade: release of gases
- European operation creates discharge
- Discharge duty with energy
- Issue pardon without resistance
- Avoid one in time for discharge
- Going out on internet quest?
- Issue certificate, ultimately leading to job
Buddy explains!

The straight part
We know that "Outflow" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case outflow = emission.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 EMISSION mean?
EMISSION noun- Something which is emitted or sent out; issue.
- The act of emitting; the act of sending forth or putting into circulation.