The most common and most likely answer to this crossword clue is the 8 letter word CATHETER
I've seen this crossword clue in The Daily Telegraph
C
A
T
H
E
T
E
R
More clues leading to the result CATHETER
- When travelling, a cert to go with the Tube
- Heading for Camden, tear off to catch the Tube
- Caught a place for surgery in the US lacking a medical tube
- Provide what’s needed to catch the Tube
- Supply food, catching the tube
- Tube of tortoiseshell perhaps not entirely straight
- Cardiff’s first theatre collapsed into drain
- Trace the damaged tube
- Clear air turbulence occurs before heater loses a connecting pipe
- Article blocking supply tube
Buddy explains!

The straight part
We know that "tube" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case tube = catheter.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 CATHETER mean?
CATHETER noun- A small tube inserted into a body cavity to administer a drug, create an opening, distend a passageway, or remove fluid.