Vessel attached to second pipe (5)
I believe the answer is:
sewer
'pipe' is the definition.
(I know that sewer is a type of drain)
'vessel attached to second' is the wordplay.
'vessel' becomes 'ewer' (ewer is a type of jug).
'attached to' means one lot of letters go next to another.
'second' becomes 's' (common abbreviation).
'ewer' put after 's' is 'SEWER'.
(Other definitions for sewer that I've seen before include "Filthy channel" , "Drainage channel" , "Disposal outlet" , "Pipe for waste matter from houses, factories etc" , "Drain - seamstress?" .)