Reddit mentions of Hopkins 08525 Graduated Level

The concept is pretty simple -- you dig a trench, line it with filter fabric, and fill the bottom couple inches up with gravel. Then you set your pipe in, establishing a 1° slope towards where it exits, and fill it the rest of the way up with gravel. Fold the end of the filter fabric over the top of the gravel trench, and then cover the top with whatever decorative landscaping you like. In my case I made a rock garden over the part of it, and a flagstone path over the other portion. This write-up on WikiHow is a good primer.

Some things to note:

• Some people will tell you to put your pipe in with the perforations facing up. Those people are wrong. Water will fill the gravel trench until it enters the drain pipe through the perforations, and the lower they are the better a job your drain will do of de-watering the soil above it.
  
• You can use corrugated pipe or PVC to build your drain. Each has pros and cons, but the upshot is that corrugated is cheaper, quicker, and easier to install. Some versions even come with a large-diameter filter sock packed full of styrofoam peanuts already wrapping them, so all you have to do is dig your trench and chuck it in. Rigid PVC pipe is harder to install, since you have to dig perfectly straight trenches and cut it to length and attach fittings at every turn. However, it will be easier to set a slope with it, it will last longer (smooth pipe walls mean that sediment can't find an easy niche to collect in) and if it does clog, you can snake it clean without it getting shredded like corrugated would.
  
• Setting the pipe at a slope is important for longevity of the system. You can install it flat, but it will silt up faster if you do. It's also something you can't really eyeball, and traditional methods for setting a slope are a PITA. I rigged up a cheap and simple method to ensure I was getting the right slope by purchasing one of these trailer leveling gauges and attached it to my level in order to get a precise slope measurement.
  
• If you're using PVC, be sure to include a cleanout somewhere so you can maintain and repair the system. Depending on how you build it (corrugated vs. PVC, slope, filter fabric installation) the drain can last from 10 to 30 years before it silts up and stops working, but with a cleanout you can extend that lifespan further.
  
• Sketch out the routing for your drain and use your measurements to figure out how much material you'll need. If the drain close to your foundation, you can also measure the amount of grade change you have to work with by measuring from the ground to the top of your foundation or the first course of siding. On a flat lot, you may not be able to get 1° of slope all the way through.
  
• You're going to need a lot of gravel. If you're hand-digging the trench, figure that it's going to end up about a foot wide. That means that for every foot of depth, you need two 50-lb bags per foot of length. I ended up putting about 2000 lbs of gravel in mine, and that was before I added the rock garden on top. If you have a truck, you can save some money here by buying in bulk from a landscape supply house rather than in bags.
  
• You're also going to have a lot of extra dirt afterwards. If you need to regrade around the house to establish positive drainage, now is the time. If you don't have a place to put fill dirt, you'll need to have it hauled away. In my case, my neighbor needed all the fill I could give him for his own landscaping projects, so I didn't have to worry about it.