When you are swapping 2 wires with a DPDT switch it works just like a "4 way".
![[Linked Image from gfretwell.com]](http://gfretwell.com/electrical/Reversing%20sw.jpg)
The problem is your idea of also using this for the on off switch. You are dealing with 2 windings and they need to both be switched. The way I see it you need at least one more pole and then it still won't really be "off" in the sense of a disconnect.
This is typically done with a drum switch.
That actually functions more like a 4p dt
Look at the diagrams at the end of this catalog page for some ideas.
http://gfretwell.com/electrical/Catalog%204258%20Drum%20Controllers.pdf
