I agree...he is using the drain screws on the bottom of the carb float bowls to drain the carbs into a glass jar.
You can clearly see that he has picked up some water. As water is heavier (higher density) than gasoline, it will separate and sink.
In addition to seeing the water, you can also perform a "Clear & Bright" test this way. Good, clean fuel should be basically transparent, allowing you to see through it. Colour is OK. Most Gasolines are naturally slightly straw brownish, but oftern have a slight amount of dye added, but should still look clean and clear, with no noticable water, sediment, cloudyness, etc. and when held up to sunlight, should have a slight "sparkle" or "brightness", ie: "Clear & Bright".
In addition to the water, this fuel also look cloudy. If it were my bike, I would be draining and cleaning the tank and petcock as well.