Me, too, OP. I got you. I’m building stuff like what you want. If you PM me an email addy, I’ll send you lots of pictures and some drawings.
The highlights:
Wash stall will be 10’ wide, and 12’ deep with tie rings set 2’ back so that water doesn’t get into the aisle.
Groom stall will be 12’ x 12’ and across the aisle, partly because I want it to be expandable into a stall later, if needed. It will have stone dust and mats rather than concrete and mats. Before it’s a stall, it will be easier on everyone’s legs. That larger groom stall/stall will have room for shelves, a vacuum and muck bucket in the corner. I wanted the grooming stall to be separate from the wash rack because I wanted a place for a farrier to work (though there will be others), a place to clip and that could handle the kind of detritus that I didn’t want in a drain. Also, it’s nice to have two horses who can see each other if they are waiting. In my current plan, those are almost across from each other. And both are near a “hang out area” where I can be cleaning tack or petting the barn cats and generally supervising (or creating a police presence that might limit pawing).
I do have a picture of a wash rack with a rail separating it from a galley-like work area with sink, cupboards and stacked W/D in a closet in the back corner. I will bet a tad of water gets over there, but not much. I have briefly rode at a barn with a wash stall next to groom stalls, just separated by a rail/shelves this way and I don’t think horses in the next bay got sprayed too often. But I’d lose my mind if someone sprayed my expensive Frenchie saddle; I’ll ask the pro who worked there longer about her experience.