You need to start with a well curried and brushed horse. I wet towels with cold water and wring them out, or take them straight out of the washer. I then put them in the microwave until you can barely touch them. I have a midget sized microwave in the barn for this. If I have a big horse or it is really cold I will get several ready and keep them in a lunch sized cooler. I tried the shampoo in the water but it offered no advantage for me. After the hot towel use a dry towel. A quick spray and soft brush and reblanket. Hot towels are wonderful at horse shows to clean ears, faces and muzzles before make-up.
I keep a midget sized microwave in the barn. I just wet the towels, wring as best as I can and then nuke the towels. I get several ready at a time and keep them in a cooler. I tried shampoo in the water before but it didn’t offer any improvement in results. Hot steamy towels also clean tack really well.
This has been our answer to the never ending static shocks for the basic /daily grooming! I curry, hot towel, brush. We have a heated grooming area, and he dries fast enough to do this lightly before riding. And he doesn’t give me the evil eye when I reach for the brush. Bonus is that a little bit of dampness helps with the static when I put on a quarter sheet too.