In that diagram, the designer assumed that the bog is lower than its
surrounding. That necessitated a deep hub, equivalent to a bottom drain. In your
bog, since it's above ground, your drain pipe is more than adequate.

Ann in Houston wrote:

Thanks, I thought that was what I was seeing. Still, the part you
explained was what was bugging me - that, and the price. I didn't realize
that they were relying on the water falling down out of the rocks to the
pipes, where it could run into the chamber. I made the mistake of thinking
it doubled as a clean out and settling chamber.
Anyway, I still think a drain is the way to go, after all. I have a
unique advantage in that we have that drain already in place right behind
the spot where this will be. If you read my drain post, tell me if it makes
sense to you. I am very encouraged by it.
Ann