Keeping Up with the Kardashians airs Sundays (9 p.m. ET) on E!

Kim and Kourtney Kardashian are sweating it out.

On Sunday’s upcoming episode of Keeping Up with the Kardashians, the sisters take a sweat test with pal Jonathan Cheban to see who is the healthiest out of the trio — and PEOPLE has the exclusive (and hilarious) sneak peek!

“So these are the vials that they sent. We have to collect sweat and go in the sauna,” explains Kim, 37, as she showcases the glass tubes.

“Are you sure we’re going to get enough sweat?” Cheban, 43, questions. “I feel like you’d have to squeeze me out to fill this in.”

Kourtney, 38, seems skeptical, but ultimately agrees to join Kim and Cheban in the sauna to prove that she is the healthiest: “I’ve never heard of a sweat test and it just sounds gross, but we do some pretty crazy things to get the information we need, especially when it comes to beauty and health, so I am definitely willing to do Kim’s test to prove that I’m healthier.”

Each donning white bathrobes, the group enters the sauna, where they sit side-by-side on the wooden bench and quickly begin to drip sweat.

“I’m sweating already, which is great,” Cheban admits.

“I feel like my legs are sweating,” adds Kim.

“I feel like a freakin’ pig!” says Cheban. “I think this is good enough. It looks like cloudy sweat.”

After the group sweats it out, they exit the sauna and cool off together while discussing the “disgusting” test.

“I think this test is a goof,” Cheban says.

“That was exhausting,” Kim exclaims.

Although she chose to participate, Kourtney suggests that they at some point take a “real test,” explaining, “I”ll ask my doctor, but I don’t want to take false results from sweat mixed with makeup and spray tan.”

While the mother of three might not trust that Kim’s test will be accurate, she does learn something from the sweaty sauna experience: “I think I definitely need to start drinking more water.”

Keeping Up with the Kardashians airs Sundays (9 p.m. ET) on E!