I put a rainbarrel in the backyard and used a diverter to move some
water from the leader into the barrel, It rained hard yesterday,
filled the entire barrel, and overflowed somewhat even though the
diverter does sort of do the job of letting the overflow go down the
leader. I know that it isn't a good idea to let water flow around the
foundation.

Not a big problem since one simple solution is to drill a small hole
in a lower part of the leader and run a hose from the overflow of the
barrel back into the leader. But I got curious about just where the
leader actually takes the water.

It goes into a ceramic (?) pipe that extends maybe two inches above
the ground and is about six inches in diameter. The leader goes into
it and is sealed with something, at least on top appearing to be just
earth.

I'm guessing it connects to the house piping and then maybe the sewer?
I don't see any pipes in that area of the basement though, so perhaps
it's a direct link to the sewer, although that's at the front of the
house. Also, there is a drain at the base of the steps leading into
the basement from the backyard that supposedly goes to a dry well but
I don't know that for sure, logically it would connect to wherever the
leader goes.

I was pretty surprised how quickly that barrel filled, it's 55
gallons. I might hook another one up to the first one since it's just
a garbage can with a hose shoved into it. The cost of water has been
going up very fast over the last few years so it seems like a good way
to water the lawn and tomatoes without running up the bill.