I have similar fermenters (13 & 8 gal) that were also used for pills. I drilled 1.5" holes in mine and I use Speidel stoppers and airlocks. The nice thing is they are HDPE. The ones with the red lids are 13 gal and the ones with the blue lids are around 8 gal. I have three blue and 2 red. They work great, I think you'll be happy with them.
Brewin' on a Medium Brewha BIAC system with glycol
"Always do sober what you said you'd do drunk. That will teach you to keep your mouth shut."