The most common and most likely answer to this crossword clue is the 5 letter word SCUBA
I've seen this crossword clue in Financial Times
S
C
U
B
A
More clues leading to the result SCUBA
- Diving apparatus son got on Caribbean island
- Type of diving ducks finally seen on island
- Diving gear stowed aboard, initially worn by youngster
- Young reporter blocking South Africa tanks
- Equipment for dive in Southern part of Caribbean
- With which one gets tanked up in holiday dive?
- Solid container using bottled air initially
- –Republic’s back to front airline supplier
- Gear used by those going down South Island
- Small country making aqualung
Buddy explains!

The straight part
We know that "tanks" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tanks = scuba.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 SCUBA mean?
SCUBA noun- (underwater diving) An apparatus carried by a diver, which includes a tank holding compressed, filtered air and a regulator which delivers the air to the diver at ambient pressure which can be used underwater.
- To perform scuba diving.