The guys from “Workaholics” better give a big thank you to co-star Adam DeVine … ’cause a porn site is offering to let them watch a smut session IN PERSON —  for giving it public props.

DeVine told Rolling Stone last week he has trouble writing at home because of Porn Hub … adding, “they know what guys like” … so the site reached out extending its open offer.

The letter says the company has partners who film close to the “Workaholics” set … so Adam, Anders and Blake can cruise by anytime to check it out.

That’s so tight butthole.