Adding a volume control to a circuit - what pot value?

I am finishing off a tonepad a-gua (http://tonepad.com/getFile.asp?id=113) and before i box it i was thinking of adding a volume control as it seems to boost the signal more than i would like when engaged, but what value of pot do i use? how do i figure it out?

The output is from an IC. Like an op amp output, it's low impedance, so you don't need a big old 1M pot there.
Look at R2 - it's 200K. You can replace it with a 100K pot. One end to ground, the other end to R1, and the center to the output jack. Use an audio taper pot. If the taper sounds weird, swap the end two terminal wires.

thanks! i wasn't sure if replacing one of the resistors with a pot before the output was the way to go as the output is hooked up both ways, i would have just put it in after where "output" is marked. i'll give it a try.