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How to install Infiltrator Septic System?

Elvis Elvis

You will have to install an infiltrator septic system or 4”PVC perforated pipe in clay ground. The public health inspector usually makes the decision after he has inspected your soil. Sewage will not penetrate heavy soil, your system will not work properly using the trench style septic system. This is why they use the more expensive infiltrator type system or the mounded septic system.

The infiltrator septic system and the mound septic system are the same systems. The only difference is, one sticks out of the ground more than the other. Can you guess which one?

It all depends on your soil which system you need. Some of these systems can cost as much as 10,000 dollars, where most will cost about 4000-5000 dollars. I recommend you get 2-3 quotes for your system before you settle on anyone.

The number of bedrooms in a home determines the size of the septic system. Your septic system design will show you how many infiltrators or lengths of PVC pipe you will need. Either you or your contractor should order and have on hand the supplies for the system. Some inspectors will let you dig down into the original ground no more than a foot, so the septic field is not sticking out of the ground so far.

The septic tank is installed exactly the same for the infiltrator septic system as it would be for the trench septic system.

Install the septic tank close to the home and in a place where it has easy access, in case you need to work on it or have it pumped. It really doesn’t make a lot of difference how far away the infiltrator septic system is from the tank.

You need to know where the lines are at all times in case you want to do some digging later. Bury the PVC pipe at least a foot or so, we don’t want it to freeze. Never bury a sewer line under the driveway, it will freeze every time unless you cover it with Styrofoam.

Now the fun begins! Dig out the area for the infiltrator septic system at the lowest part of your lot. It will be easier to slope the field when it comes time for landscaping and also it will be below your drilled well. Never put a septic system in a swamp or wet area. When you dig down into the ground a foot, place or push the fill to the outside of the area where you want your infiltrator septic system. You need to dig the ground down so it is 6 feet below the outlet hole of the septic tank. This will allow you to fill it back up again with 4 feet of gravel and leave enough room for the infiltrators that will sit on the gravel.


  Infiltrators are 12 inches high, so the inlet hole must be higher than the outlet hole of the septic tank. If you choose to use 4”PVC pipe over the infiltrators you only need to be 4 ½ feet below the outlet hole in the tank. You are going to build a burn or a wall of mud to hold the gravel you will be hauling in for the infiltrator septic system. Most systems are 30 X 50 feet and the depth is usually about 4 feet. To figure out how much gravel you need for the system multiply 30 X 50 X 48 and divide that by 324. This equals 222 yards of gravel, which is about 18-19 tandem loads. Building lots are in different shapes and sizes so you will have to build your septic system to fit your lot.

You will need to maintain access to the septic system for gravel trucks. It takes a long time to carry that much fill any distance. I have many times made the road so the trucks could back right into the bed. (Don’t get stuck!) Every lot is different so you will have to deal with yours the best way you can. Haul all the gravel in that you need to build your septic bed. A small dozer is required to level the gravel. The gravel bed doesn’t have to be perfectly level but should be close, so try to maintain 4 feet of gravel over the infiltrator septic area.

Not a lot of people do, but I would compact the gravel before I placed the infiltrators or the pipe on the pad. Four feet of gravel pushed in loosely will settle 8 inches. The equipment will not compact the gravel enough. If the gravel settles too much the infiltrators could pull apart and make a mess of the septic system.

When you are done leveling and compacting, place your infiltrators, or pipe, on the bed and build the system that you have designed on paper. The 4 inch PVC pipe coming from the septic tank to the infiltrator must sit on solid ground. You must make sure the pipe doesn’t settle and destroy your system. Fill in around the end of the infiltrator and compact. Your diagram and contractor will help you connect all the components of your system.

How to install Infiltrator Septic System?


After it has been inspected and passed you can backfill it. The best way to backfill the infiltrator septic system is with an excavator. The excavator can place material all over the system without driving on it. This system needs to have good soil for the top because gravel will allow rain water to seep into the system. The rain water cannot penetrate the field or your field will fill up and your septic system won’t be as efficient as it should be. Once you have it covered, level it off with the bottom of the excavator bucket.

After the earth has settled between the infiltrators you can bring a small dozer in and level it up and get it ready for grass. The grass will keep any water from getting into the ground and will also pull moisture out of the septic bed. Have you ever seen a lawn really green in some spots and not others? This is because the grass needs water in dry times, so the roots pull the moisture from the septic bed.

Here is an example of why infiltrators are better than PVC pipe. When you use PVC pipe you need to use drain rock as well. When you use infiltrators you don’t need any drain rock. This system can be built with a bull dozer. After the bed is built you lay the infiltrators out in rows and cover them up. The PVC pipe needs to lay on drain rock and needs drain rock over it.

If you consider all the time and materials that are involved in building a septic bed with PVC pipe, then the infiltrator septic system may not be a bad idea after all. I suggest you get prices on both ways and if there is little difference I would go with the infiltrator septic system.