Tower in every detail penetrated by disastrous bug (7)
I believe the answer is:
tugboat
'tower' is the definition.
(something which tows)
'in every detail penetrated by disastrous bug' is the wordplay.
'in every detail' becomes 'to a t' (I've seen this before).
'penetrated by' means one lot of letters goes inside another (I've seen this in other clues).
'disastrous' indicates anagramming the letters.
'bug' anagrammed gives 'ugb'.
'toat' placed around 'ugb' is 'TUGBOAT'.
(Other definitions for tugboat that I've seen before include "Vessel drawing" , "Drawing craft" , "Ship pulling a larger one" , "Small vessel pulling a big one" , "Powerful vessel used to pull larger ones" .)