Getting IDLE to use correct Tcl/Tk on MacOSX 10.6?

[Gregory Ewing]

I don't normally use IDLE, but I had occasion to use it
on MacOSX 10.6 to answer someone's question, and of course
it didn't work properly due to Apple's broken Tcl/Tk.

I followed the advice to install ActiveState Tcl 8.5.18.0,
but my Python still wants to use Apple's Tcl.

How do I persuade Python to use the new one I've installed?
It's a framework install of Python 3.5 that I compiled
myself. Do I need to rebuild it to get it to pick up the
right Tcl? Or is there an environment variable I can set?

-- 
Greg