Demonstrating how to enter pipe (7)
I believe the answer is:
showing
'demonstrating' is the definition.
('show' can be a synonym of 'demonstrate')
'how to enter pipe' is the wordplay.
'to enter' indicates putting letters inside.
'pipe' becomes 'sing' (Pipe up means sing up).
'how' inserted inside 'sing' is 'SHOWING'.
(Other definitions for showing that I've seen before include "(Film) presentation" , "Demonstrating" , "performance" , "Presentation; visible" , "Evident" .)