How to confirm a memory leak

[Norman Goldstein <normvcr telus net>]

I'd like to understand how to confirm a potential memory leak in gtk3.  
Valgrind shows a definite leak, and "top" shows a steadily increasing 
resident set size (RES).  However, as I have come to understand, due to 
how gtk/glib uses slices for memory management, and how the main loop of 
gtk plays a part, things are not as straightforward as I have just 
outlined.  Is there a definitive guide, "How to confirm a memory leak in 
GTK"?  I have only seen various relevant pages on the net.