I had a bit of exposure to large print processing as a young teen apprenticed for a few weeks one or two nights to an older guy who made photo murals - generally 36" high by several feet long on mural weight (heavier than DW) fibre based paper. Just at the beginning of my interest in photogrpahy. Old british guy who had worked in photo reconnaisance in WWII, Fred Noakes. Long gone by now. I would love to know what became of his gear.

He had an epoxy piant coated piece of plywood, with a lip on the lower edge (i will call it as Fred did, as the platten), that sat on a braced affair on a cart. The cart made it tall enough to allow the lip to drain into the sink, or a bucket placed in the sink. It could be taken apart when not needed.

After exposure, you would untack it from the wall, and roll the paper up emusion side in. Start processing it with the leading edge of the mural at the downhill end of the platten. You would wet the platten with a wet sponge so the paper would stick to it, then, rubber gloves on, lightly rub the face of the emulsion with a sponge dipped in a bucket of Dektol, more dilute than normal. Once the first part was soaked and coming up, roll it up, unroll more and start on the next section.

Then look over the results, and see if any areas were weak, and needed more developer rubbed on. If not, hose down with low pressure running water and a clean sponge to wash/stop the developer. Then fixer one rub down, then fixer two rub down, then three passes of washing. The later two often the next morning.