For a start, many a tube gets bent (5)
I believe the answer is:
debut
'for a start' is the definition.
(debut is a kind of start)
'many a tube gets bent' is the wordplay.
I cannot really see how this works, but
'many' could be 'd' (Roman numeral for 500) and 'd' is found in the answer.
an anagram of 'tube' is 'ebut' which is within the answer.
No letters remain.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for debut that I've seen before include "First attempt" , "Tubed (anag.)" , "The coming out of a society girl" , "Initial appearance" , "First public appearance of performer" .)