I had a vacuum problem on an Orca cooler . It can get very had to get the lid open in warmer months. I purchase a Grizzly valve drain plug, Machine Alum, its has a pressure valve built in. WWW.Grizzly-valve.com or Ebay. A much larger area for gripping while removing than stock plastic plug. Another after market product that is awesome. It fits Orca, Yeti, Engels and I suspect most other gasket coolers.
Good to know, as I love my Yeti, thanks.