The Allure of the Sewer

I usually enjoy Theo's obsessions. For a while it was plants, which I enjoy. Then music, which I also enjoy. Lately it's numbers, which are also reasonably interesting. But his newest obsession befuddles me: sewers. I cannot tell you how many times a day he asks about sewers, and how much time he spends talking about them. Something like this occurs multiple times every day:

Theo: Mommy, what's that?
Me: Theo, you know what that is.
Theo: A sewer!!
Me: Yup.
Theo: What's in the sewer, Mommy?
Me: I don't know. Why don't you tell me?
Theo: Um...some sticks and leaves. And pee and poop. And scary mans!
Me: Okay... [praying that the sewer discussion is over]
Theo: What number do I have to be [a.k.a. how old do I have to be] to go in the sewer?
Me (knowing that a vague answer will never fly with Theo): Twenty-two.
Theo: When I am 22, I will go in the sewer!

This is all fine and good, but now he's telling random people that when he's 22, he's going to go in the sewer. And so I have to explain that his current life goal is to work in the sewer. (He claims he's going to "plunge lots of stuff!" in there.) Alternatively, he's going to go to school to work for PG&E with "electricidity." Ah well, either one probably pays well, so go to it, my boy! But you can have your own bathroom and shower if you choose to work in the sewer....