These scenes are from season 1 episode 3.
1 minute in the episode, we see Mike Vogel masturbating. There is no full frontal, just his facial expression.
3 minutes in the episode, he is taking a shower and we see his butt when he leaves the shower.
7 minutes in the episode, we get a great view of Adam Demos' butt. Very detailed, we can see the little bit of butt hair he got.
19 minutes in the episode, we first see Mike Voget's butt in the gym's shower. He went to the shower to check on Adam Demos.
Then we get an amazing view at Adam Demos' HUGE circumcised penis. We also get a quick view at his butt.
41 minutes in the episode, we quickly see Mike Vogetl's butt as he is making love in a car.
Finally 48 minutes in the episode, we can another good view at Adam Demos' butt.
In an interview with Collider, the series creator explains that no prosthetic was used and this is indeed the real huge penis of Adam Demos that we can see in the episode.