This video and this way of showing how to set up a tubeless tyre is exactly why so many people hate tubeless tyres because this method is open to failing and sealant going every where. It is very easy to seat a tyres beads into the rims without the sealant at first. Then remove the valve core and add the sealant through the valve. Then just pump the tyre back up and as the tyre is already seated, the sealant stays in the tyre.