What is the reason you want to "clear out the tummy" and why, specifically, do you want to use a bran mash to do so?
Knowing what you are trying to accomplish (more clearly than stated in the OP) will help a lot in directing any response.
The vet said my horse has been laying down because of his upset tummy, however he did not hear any sand swirling in his gut so he wants me to start him on a few bran mashes a week. So I'm looking to see if someone knows of a good bran mash.
Wheat bran, oats and sweetfeed or oats is pretty traditional, but you can "mash" most other feeds too. If you feed a pelleted ration, just make it super sloppy with water.
If he has an upset tummy, did the vet mention ulcers or any other ailment? A mash is not going to hurt, but I doubt it would cure. Maybe try putting your horse on probiotics or a natural ulcer treatment containing calcium?
I figured it was obvious when I had the vet out to do a physical that he took fecal and blood, he did and I will be calling in about a half hour to see what the tests showed.
And from what my vet here and my past vet from Florida said, you can hear the sand swirl with breaths, never heard it myself but somethings gotta be there if 2 vets, in totally different states said something about it. And we do have sand and dirt here in MI, more now when the grass is coming up and again in the winter when everything dies, dirt does the same as the sand, builds up and causes colic.
As far as ulcers, we have not yet gotten to there, I will ask about it today if nothing came out of the other 2 tests.
We are trying the mashes first, to see if he improves, if not in 2 days we will pursue other avenues.
For my mash I used
5 cups Wheat bran
1 cup Purina Senior
1 cup Safe choice
And wetted it til it was sloppy mush.
The vet said to put these 2 feeds in with the mash if I wanted since they are fiber rich and will help.