The army camel joke reminded me of this (slightly NSFW)

A guy looking for a job finds that a certain mill is hiring lumberjacks. So he goes out to the mill and talks to the foreman who tells him all about the job, pay, and housing for all of the lumberjacks. Everything looks perfect and the guy is ready to go to work at once.

But when he was walking around he noticed that there weren't any women around. So he pulls the foreman aside and asks him what everyone does for sex. The foreman laughs and brings him over to this big tree that has a hole in it. "This is the fucking tree. Whenever you get horny, come over and put your dick in the hole and fuck away. Trust me, it does the trick every time." The man thinks it's kind of odd, but takes the job anyway.
The days go by and soon the man gets horny. He thinks about taking it out on the tree, but it still seems weird to him, so he goes to his room and jacks off. A week passes and the guy gets hornier and hornier and jacking off isn't enough for him. So finally he figures, "What the hell," and sneaks over to the fucking tree in the middle of the night, whips out his dick and puts it in the hole. To his surprise, it feels great! Soon enough he starts to fuck the shit out of it. After a great session he goes back to bed with a big smile.

The next day after a hard day of work, he makes another visit to the tree and it's even better this time. Again he pounds away at the tree. He can't believe how amazing the tree is and wonders what kind of magic tree they have. Things just couldn't get better for him.

The following day, he runs to the tree after work, hurriedly takes out his dick and puts it into the sweet warm fucking tree. The tree just gets better and better everyday. He goes at it again, and afterwards can hardly walk.
The next day all he can think about is going back to the fucking tree. Every tree that he cuts down is one less tree in his way of the fucking tree. Finally the day is done, and he takes off for the tree. Pulls out his dick, grabs hold of the tree, and shoves it in. Nothing. The man is shocked. He tries again, but still nothing. Feeling very frustrated, the man storms off to the foreman. "What's wrong with the fucking tree? I've been there three times already and it's been better each time, but today, I ran up to it, stuck my dick in and nothing happened. What the hell happened?" The foreman thinks for a second and then says, "Oh yeah, I know, didn't they tell you? Today's your day in the tree."