How to put downspout underground

I have been naughty... I have been doing some landscaping instead of making jewelry... I thought it worth blogging... According to our design, the two downspout at the back of our yard will be in on top of a walkway... so, that's a no-no

My task... to put the down spout underground.  I learned with Colorado rains, 3" pipe is good. Hubby already dug with a trencher. The trencher size... 3". It's a bit too snug for the pipe so I have dug it wider.

I use the black flexible downspout pipe I got at Home Depot ( or Lowe's). I need a connector from 2x3 downspout to a 3" pipe, a strainer (to prevent unwanted critter from coming in). Not tape or glue required.

There is groove in the pipe that you can attach the pipe and the connector easily. 

Perhaps, the hardest part is digging the trench and making sure it's sloped away. I use level to make sure that the pipe is sloping out. 

Here's the picture of the almost final result. It took me a day to work on 2 downspouts and a day to dig the trench. What do you think?