22 gallons average, hey, that's 40 camemberts a day, $100,000 a year at $7 each!
Oh well, waste milk products are likely not legal to sell, but you might be able to raise a few hogs on the side with that much "free" feed instead of giving it away, or get a few more calves, or fix what's causing so much waste milk. But yeah, it has a production cost, so it should have a price too. If you want to sell it, you need to find the correct balance so the customer will buy it cheap instead of not buying it at all. Some dairies/dairy processors buy waste milk, maybe check with yours, but it would probably not be worth collecting and selling so little at their cheap prices.

Google "managing waste milk," lots of useful information and PDFs.