The most common and most likely answer to this crossword clue is the 8 letter word PLUMBING
I've seen this crossword clue in Financial Times
P
L
U
M
B
I
N
G
Buddy explains!
The straight part
We know that "trade" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case trade = plumbing.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 PLUMBING mean?
PLUMBING noun- The pipes, together with the joints, tanks, stopcocks, taps and other fixtures of a water, gas or sewage system in a house or other building.
- The trade or occupation of a plumber.
- A system of vessels or ducts in the human body, especially the genitourinary system.
- Practical, concrete work serving to support other work.
- A Murasugi sum where each disk summed along has its boundary subdivided into four segments.