Flex Seal Liquid

Flex Seal Liquid® is a thick rubberized liquid that you can pour directly into cracks, stop leaks, and dip your tools in (for whatever reason).

In the advertisement, Phil makes an airboat out of a screen door, and waterproofs it with Flex Seal Liquid®. He rides the boat in "alligator infested waters" for the day.

https://www.youtube.com/watch?v=VikGZ5T-S7U