I typically hate runnels but if you are wedded to this dishwasher concept I think they make sense for you. I don’t understand where you say you want the counter over the dishwasher to be a separate piece?

No to the runnels. I don't like the look, and they look hard to clean (as you put it - germy). Just set the DW racks in the sink to dry or on top of a drying mat set on the countertop.

While I do like the look of runnels, I’ve seen them in action. Unless your’re vigilant about wiping them out after each use, they do get gunky and slimy.

I’m all in on drying mats. We use them ourselves. They come 2 or 3 to a pack on Amazon. Reversible . Machine wash and dry.

Drying mats

The rack won’t fit in the sink - they are about 20” x 20” (roughly). And the sink is being used to pre-rinse the dishes being loaded into the second rack. For highest speed, you use two racks, one is loaded and unloaded while the other one is being washed.

What I mean by “separate piece” is: my DW enclosure is a separate piece that connects on one side to the dish storage cabinet. I can put one piece of countertop on that DW enclosure piece, and a different piece on the adjoining dish cabinet. There will be a seam between those pieces; I’m not sure if that will bother me.

I’d likely make the runnell / drainboard countertop piece from copper formed over plywood, with grooves in the plywood for the runnells.

So the runnells can’t be very sharp-edged or deep; they’ll be easy enough to wipe clean, and copper is supposed to be antimicrobial.

If that proves impractical, I can have it fabricated in stainless steel. But a plastic drain tray that gets pulled out of storage and placed on the counter will work as well as a built-in runnell/drainboard, so I don’t know that I would spend the money to have the latter fabricated.

Is that going to sit on top of your other counter or you are going to seam that in between two other sections of counter? If you are paying for custom why not get a custom sink made with integrated runnells?

I’m sorry, Hallet, it’s hard to explain but the pic below may help. The “sinks” are just temporary plywood/epoxy, pending my actual custom sinks being fabricated. There are no countertops yet. The DW will be between the right (wash) sink and the right most (dish storage) cabinet. So the bit if countertop that may have runnell/drainboard is the piece above the DW. It will overlap, thus drain into, the sink.

why couldn’t the dishes stay in their rack after washing, to air dry? If there is a door, open it till they are dry?

This is like a commercial glass washer? I think because the inside is so hot and there is going to be water condensed all over the inside (which is usually stainless?), that the inside is pretty humid and it makes sense to take out the plastic rack (which is kind milk crate like in construction?) so that the hot glassware/china, sort of dries itself out in the air...

There is only one rack, usually so the speed is part one, but having to do multiple loads sometimes is part two.

Palimpset, that is exactly it. It is hot and steamy inside the machine. The rack needs to be removed to a different place, like on top of the counter, for the dishes to air dry. My machine rinses at such a high temp that if you lift the rack out as soon as the rinse is done, the dishes are dry in a couple minutes.

Is there any advantage (other than the warmth of color) to using copper rather than more traditional stainless? I’d have a lip / edge on the front and back and slant it towards the sink similar to standard commercial set up.

I had a recessed, sloped drainboard without runnels in my last counter and it worked well.

lisaam, it is partly an expense thing. I can DIY copper countertops but not SS countertops.