Tools & Materials: All that you will need to build a waste composter is a shovel, a saw, a drill, 4" pvc pipe, and a vessel of some sort.
First find your vessel. I decided to use a salvaged plastic 55-gallon barrel and give it a third life. A 5-gallon bucket or a trash can would work if you have a small dog. Rather than recycling the barrel I simply reused it. I got it from our local coffee roaster and used it as a leaf composter for a couple years. Be careful that you don't use a barrel that may have had toxic chemicals in it. Mine used to be full of French vanilla flavoring. That stuff is fairly harmless.
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Step 1: Preparing the Vessel
If you are using a barrel you will need to cut the top off. The open end will become the bottom of the compster. This will increase the surface area that is exposed to the soil and allow rain water to drain easily.
Next cut a circular hole into what will be the top of your composter. I cut a 4-inch hole into mine because I decided to use a 4-inch inside diameter (ID) pvc pipe as the access port for my composter. It's good to have a hole large enough to allow the dog waste to fall into the vessel without the need of a push-stick. The 4-inch ID pvc fits perfectly over the 4-inch hole without the danger of falling in. I was able to find a waste cut piece of pipe that was headed for the dumpster.
Step 2: Dig It
This is the most difficult step. Dig a hole large enough to fit the composter into it and deep enough to bury it a foot or so underground. Keeping the composter below the ground level will help keep it from freezing as easily during winter. Be sure to keep the topsoil separate from the rest of the soil.
When the hole is dug try the vessel for fit. Put a straight edge over the hole in order to get an accurate depth measurement. This measurement is needed to calculate the required pipe length.
Step 3: Access Port
After back filling the hole the only part of the composter showing will be the stickup portion of the pipe. I plan to put a rubber cap on the pipe to help control any odors. You now have a pet waste composter that is large enough to handle the waste from a big dog and yet safe. Unlike other designs that I have seen, nobody will be able to fall into this one. Job well done.
Step 4: Drop the Poop
It should be quite some time before this composter besomes full. When the composter is full I can simply take the topsoil off the top and pull the barrel out of the hole. At this point I can either use the compost as lawn fertilizer or simply bury it. Either way we have already helped preserve a little bit of our precious environment.