Volume Pedal in Dirty Shirley loop

Hi,

I want to start using a simple volume pedal in the effects loop of my Dirty Shirley.

Can anyone advise if there is a specific type I need?

I was unsure if the pedals are designed differently if they are used in the loop as opposed to between guitar and amp input?

Any help appreciated before I buy one.

Use a low impedance pedal. Boss fv500L or fav-30L or any other low impedance pedal.