sediment in shower faucet, removal?

Hello all,
Periodically I have to take the screens off my faucets to remove small particles of sediment. I can tell when it's time to do it because they really affect the flow.
So, lately the tub/shower pressure is very low. I've removed particles from all other fixtures and flow is fine every where else.
My question is, how do I get in there to remove these pieces? The shower hardware is Moen, and there's no access panel behind the wet wall. I've tried taking off the front panels to peek, but nothing obvious there.
How do I get in there to take out the gunk that's obviously trapped? I know it's in the valve area because tub and shower pressure are both low.
here's a quick pic of the setup.
Any ideas??
P.S. please response to the group, unless you feel like figuring out my email :)
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