There's plenty of information on how to install gutters, including:
I wanted to make this Instructable to show how I hid my gutter downspouts. It took about two full days of work. Parts were pretty cheap, I think total cost was only about $100.
Shovel, level, 2x4, rubber mallet, chisel, utility knife
PVC pipe, various PVC fittings, purple PVC primer and glue, black corrugated tile and fittings, three downspout adapters, one animal guard, one sack of Quik-rete.
Step 1: The Problem
About an hour after finishing my gutter project this summer I tripped over one of the downspouts. Since it is thin aluminum, it immediately bent in half. I straightened it out but it still looked awful. I realized that while my guttering was done, the real work was about to start.
Step 2: The Plan
The rainwater from the back half of the property slopes down to the alley, which has a storm sewer. The house sits in the front half of the property, which is flat. Before installing gutters, rainwater from the roof fell to the ground and didn't flow anywhere before soaking in to the soil -- hence, large spring rains lead to water in the basement. I wanted a good way to get rainwater from the roof as far away from the house as possible.
While the house sits on flat ground, there is enough slope in the back yard for this project to work. Water flows downhill so you have to have some amount of slope so the water will run somewhere.
My plan was to use 4" PVC pipe, with fittings, to make a Y-shape away from the house. I settled on this design because I wanted as few angles as possible, so that any speed the flowing water picked up would not be slowed down by making a 90 degree corner.
Since black, flexible, corrugated pipe:
is cheaper than PVC, and easier to transport, I transitioned to that shortly after the arms of my Y met up. I went with non-perforated because I don't want any tree roots clogging it up and I'm not worried about picking up any groundwater. Plus, since the Corex is flexible, unlike PVC, there is the option to steer around any obstacles. I didn't have to do that, but I did have a gentle curve in the course to the alley.
Step 3: Get Digging!
Next, whip out the shovel and dig a trench. (This step is easier said than done)
This will really get the neighbors asking questions, as it will look like your goal is to destroy your yard. My solution to this problem was to ignore them as much as possible and just keep digging. I ended up digging about 120' long in 4 hours.
I tried to save the grass into big clumps so that I could more easily re-sod at the end of the project. Re-sodding is crucial if you want the finished product to look natural. My goal was to not be able to see where I had trenched when I was done.
The deeper the trench you can dig, the better. I live in Minnesota and the frost depth last year was 7', way deeper than I could ever dig my trench. I settled on about a foot of depth, enough to keep it well buried but obviously it will still freeze in winter. This was about the deepest I could go with the slope that I had to work with and the way that my discharge end was going to work.
When I thought I was done digging the trench, I used an 8 foot long 2x4 and a level to make sure there was some slope to the bottom of my trench. I laid the 2x4 flat on the bottom of the trench, placed the level on the 2x4, and every 5-10 feet worked my way from the alley to the house, checking the level as I went. Not all parts had slope, some areas were flat, but no parts sloped uphill -- good enough for me!
Step 4: Assembly & Backfill
I didn't take enough pictures of this -- sorry! But I laid out my PVC pipe and fittings into their approximate shape, cut pipe to the necessary length, and used purple primer and PVC glue to connect the PVC parts. The fittings I used were a Y for the connection where the two lines connect, two 90 degree angles, and two couplings to connect pipe. I used 4" PVC and fittings because it was readily available, but any size would potentially work.
Once the PVC was glued I set it in the trench. I used a 3"-4" stepdown coupling on the end of the PVC, and put my black corrugated pipe around the 3 inch end. It connects fairly well, so the backfill was enough to hold that in to place. I rolled out the rest of the black corrugated pipe in to the remainder of the trench, and backfilled the whole thing.
In the pictures you can see how I connect the downspouts to my PVC system. On the house, I used downspout adapters with leaf guards.
Since my in-ground pipe ran right past the garage, I had the garage downspout dump in as well. To do this, I cut the black corrugated pipe, added a T, and aimed the pipe upwards to the downspout. For the garage, I used a downspout adapter without a leaf guard since there aren't trees close enough for that gutter to get clogged up.
Step 5: The Discharge End
This is the most important part of the project, as it needs to slope downhill and the water needs to go somewhere after it exits the pipe system. The alley of our house is slightly lower elevation that the property and it has a storm sewer. This was the perfect setup, as all I had to do was get water to the alley and it will flow safely to the storm drain.
The picture shows an asphalt embankment that is the foundation for the garage. I dug the trench immediately behind the garage. To get the hole in the asphalt, I used a rubber mallet and a chisel. It took a few hours of pounding to the get the hole shaped the way I wanted it.
Once the hole was done, I laid the end of the black corrugated pipe in it. I mixed up some Quik-rete, patched the hole in the asphalt, and sculpted a little discharge chute as shown in the picture. Then I put in a little removable grate to keep the chipmunks from exploring the pipe I so painstakingly installed.
At this point, I was done! There was just the little matter of waiting for rain to test my work. I didn't have to wait long...
Step 6: The Test
It rained about 24 hours after I was finished. When I went out to the alley and saw water flowing out of my pipe, I yelled, "It's alive!" like I had just brought Frankenstein to life. At least since it was raining all the neighbors were inside.
Step 7: Finished!
I re-sodded the grass chunks when I was done. Re-sodding was probably the most time-consuming aspect of the project but was well worth it. Two weeks later, I can't even tell where my trench runs through the yard. It looks great and there are no downspouts to trip on. Best of all, now the roof water, which used to end up in the soil next to the house, goes straight to the storm drain.