Simple.
Just ask the customer to provide a bucket of hot water with some Flash or Jif (Cif or whatever it's called), and two cloths.
A soft brush is a help too.
Use one cloth as a wet washing cloth and one to dry and wipe clean.
A brush will get in all the gaps, if you can get one.
I find it helps to let the next bit you're doing soak for a few mins, so slop a load of water over it, or even soak with your sprayer.
Then it's softened up and wipes off a treat.
I enjoy it. You can always get a good price and the results are very satisfying.
Makes a nice break from windows too!
I've thought about officially offering it to customers...
Cheers, Roger.