They touched on it. It's no secret. Septic systems aren't brain science. Anywhere rural has them. My Uncle has one in Muskoka. It's just part of life. Most normal rural non-alt-homes have them.

Naturally each system may have different configurations and needs. Some houses are designed so the grey water is economized so washing dishes drains into the indoor garden. That means you may not want too much meat rot going there nor toxic soaps. Poop might even be recycled in composts.

In their desert I wouldn't let water go.

Like Bucky Fuller said, "Waste is a resource we haven't found a use for."

They didn't get into the heat-sink part of the tires much. There are lots of other docus like this. Lotsa channels too.

Off-grid living is getting stomped on. Florida especially recently. Don't know why there.