They don't drain to waste. Excess nutrient accumulates in the coco substrate, they throw it away every run and use fresh. They haul in coco by the semi full. Not exactly environmentally sound, but Boulder County prohibits them from pouring nutrient water down the drain so it's the only solution left.
Somewhere earlier in the thread, Merlin answers a question and says they do drain to waste coco, which is my preferred method. I have always associated DTW as having a 15%-ish off-flow, hence the drain to waste, that's why I was looking for drains or water on the floor.
So I guess they're actually just watering? Still there has got to be some spillage, especially when they move to drip feed as not every plant has the same uptake, and container, the same holding capacity or absorption rate.
Regardless, even the visible floor between the containers looked especially clean. Unless they're constantly lifting the pots off the floor and wet vac'ing or sweeping between them, I don't know how it continues to look so tidy.
EDIT: What do they do if they need to flush?
I've spent more $ and time designing and building DTW capture systems for large-ish grows than I care to contemplate. So I guess I was hoping that there was some secret I was missing in the pictures.
I didn't know about that law about dumping nutrient water down the drain. I like that. It's always been a pet peeve of mine, dumping all that stuff into the water supply. That's how you get algae blooms and contaminated drinking water, especially in the more rural grows; runoff gets dumped into septic systems or pumped into streams.
BTW: I actually just finished reading an older, long thread about cmh that you spent a lot of time in. Lot's of interesting back and forth and I learned a lot about led's there from your posts. I'm currently contracted to do a 144 plant build, caregiver plant count restrictions account for the peculiar number, and you almost had me convinced to try some of the cob led's in lieu of the 315's I usually like to run for veg..
Not for a client, but maybe I'll try some in a smaller personal grow. Thanks for spreading the knowledge.