Drain top of ulcer in Texas hospital complex (7)
I believe the answer is:
exhaust
'drain' is the definition.
(exhausting is a kind of draining)
'top of ulcer in texas hospital complex' is the wordplay.
'top of' suggests taking the first letters.
'in' means one lot of letters goes inside another.
'hospital' becomes 'h'.
'complex' indicates an anagram.
The first letter of 'ulcer' is 'u'.
'texas'+'h'='texash'
'texash' with letters rearranged gives 'exhast'.
'u' placed inside 'exhast' is 'EXHAUST'.
(Other definitions for exhaust that I've seen before include "Car part for carrying away gases - would make you tired" , "Empty" , "Tire utterly or fumes-dispersing device in car" , "part of car - > tire?" , "Car's fume pipe" .)