Flesh Water has five easy achievements that require some light grinding. If you don’t feel like experimenting to find the four different endings, here’s how to get them plus the Welcome to the Community achievement.
To trigger the Predator achievement, go to the right edge of the sofa while making your way back. I’m not sure this is the only way to do it, but it’s how it worked for me.
Spraybottle: on the Lobby desk, to the right. Use it to clean 3 stains in the Lobby and 1 in the Utility room.
Trashbag: click the left-most door, the trashbag is on some boxes to the left. Use it to clean the pizza box on the desk in the Lobby, something on the floor (a banana peel?) near the Utility room door in the Lobby, the rusty cans (?) on a Lobby chair and more rusty cans (?) outside by the truck. Take the trash all the way to the right (past the Pool Room door) to the dumpster.
Keycard to Pool Room: on the left-most chair in the Lobby.
Chemical Room: Left-most door in the pool room. Gun is located all the way to the right on some boxes.
Other: Falling / jumping in the pool, while hilarious, will not result in an achievement or funny scene. The game will reset to right before you fell / jumped.
Man, you spelled everything wrong! To get the Predator ending, you need to select the third lamp on the left (or the first on the right), do not forget to take the gun, and on the way back, stand on the left edge of the sofa! Accordingly, in order for the ending of the victim to fall out, you need to stand on the right edge of the sofa!