Should you have a riser on your septic tank

A septic tank riser is a pipe that brings drain water from the tank to the soil surface. There is one riser for each fixture in your home or business, and they all discharge into a leach field. A riser is either 1½″ IPS (iron pipe size) or 2″ ABS (black plastic size). Risers should extend at least 12 inches above the ground surface and be filled with gravel or crushed stone graded to drain back into the tank. The top of the riser must slope toward the drainage field to not become a stagnant water source where mosquitoes breed!

An example of a properly installed system: On this diagram, you can see how a concrete slab was poured around the septic tank, and the risers are installed. The risers are attached to the tank with 2″ ABS, or 1½″ IPS clamp fittings or straps.

Should you have a riser on your septic tank, Zazzy Home

A poorly constructed system: No gravel was placed around the riser, so water could collect at the top of it. This is a very dangerous installation because any amount of pressure on the top of the riser will force water into your leach field lines that have holes in them! You can see that not enough trenches were dug either. Also, notice how close these panels are together – you’re supposed to have 50 feet between each panel.

One way this system fails is if someone drives too close to it (especially driving an RV!), they’ll hit one of the risers and make a big hole in it, allowing septic tank effluent to escape.

How do I find out what size my riser is?

A 1½″ IPS riser will be stamped with the number (thousandths of an inch) “27,” and a 2″ ABS will be stamped with the number (thousandths of an inch) “21.” If you’re not sure how to check your riser or don’t want to get that close, call us, and we’ll tell you where they should be located and their size. Or you can look underneath your concrete slab from inside your crawlspace opening – Risers are usually accessible from underneath. Why are risers important?

A riser is your “first line of defence” in protecting your leach field against damage due to root intrusion. Since they are usually made of 1½″ or 2″ plastic pipe, they can withstand a tremendous amount of abuse from plant roots, which could shorten the life of screws used for fastening panels together, and this type of root penetration into septic system drainage lines could cause them to clog up much faster than anticipated.

Root-proofing your risers by placing gravel down around them will protect their tops from being pushed apart by grass growth when it goes dormant in winter. Also, keeping grass away from the top half-inch or so will prevent excessive mulch build-up in summer.

Should you have a riser on your septic tank, Zazzy Home

Where should risers be located?

Risers should go vertically down from the concrete floor of your septic tank, not on an angle. They can be installed on both sides of the tank if needed to get them above the grass line. However, this is not recommended because adding more potential failure points in your system – two riser holes instead of one means twice as many chances for leaks! Also, risers should never be placed inside a “crib” of wood or other permeable material that might allow effluent to dribble into it and evaporate there before reaching the soil surface.

This will trap scum at the top of your risers which can cause slow infiltration of water into your leach field lines over time.

This is the slab for a three-bedroom home, so there are three risers placed in it. Note that they are not close together – 50 feet of clear space must be left between each riser to allow adequate infiltration down into the soil before water can escape through an open drain field line.

How high should risers be installed?

Risers should extend at least 12 inches above ground level because anything less will encourage “splash out” when it rains, and lawn sprinklers hit them! Also, if you have grass growing around them, it’s very easy for someone to drive up on top of one, thinking no harm will be done – but you could end up with sewage in your backyard or in the street, which is definitely harmful.

A lot of people are under the mistaken impression that it’s OK to have grass grow up against risers because water can’t collect at their tops and cause a backup in your system. This is not true! When water collects on top of them, they fill up like buckets, and when you step in one (especially in winter) with snow and ice around the riser hole, you could slip and fall in with all your weight – imagine the damage that would do to your septic tank or leach field piping!

Are septic tank risers a good idea

Although many people opt for risers, they are not always necessary. If you feel that you need to see what’s going on inside your system regularly (or if you wish to avoid having to lift up heavy lids upon occasion), then risers may be needed – but they’re definitely not recommended because it’s much better to build an accessible above.


This is probably much more costly than installing simple 3″ PVC sewer pipe drop structures with screw-top covers, but it provides easy access and allows all effluent to flow away from plantings without creating any problems. These normally last about 10 years before you have to replace them.

There is plenty of anecdotal evidence that septic tank risers can cause problems if installed incorrectly, especially where a large load of effluent enters the system from newer homes. Newer homes may have large bathrooms with drain fields to handle all water from toilets flushing into them. If poorly designed, these systems could overload the capacity of existing piping and present difficulties that would be expensive to correct.

Should you have a riser on your septic tank, Zazzy Home

In older homes, significant problems were typically avoidable provided risers were sized adequately and designed with proper clearances between riser hole walls and vegetation to allow adequate wastewater infiltration before it reaches the pipe field lines. However, problems also occurred when grass was allowed to grow against riser holes so long as sewage was held in the riser. This became a breeding ground for mosquitoes and flies and often resulted in significant odors, which could become unbearable.

As we mentioned above, there is little or no hard evidence to suggest that risers can cause problems on their own – it’s more likely the system as a whole causes problems by adding additional wastewater volume quickly where older piping is used. If you’re still not convinced of the disadvantages of using risers, try this: if you have access to your leach field lines at all times with easy riser access, then why would you need a leach field inspection?

Why You Shouldn’t Use Septic Tank Risers

Septic tank risers provide a back-door entry point into your septic system. Unfortunately, this means that anything going down a drainpipe or toilet can end up coming out of a riser – which is a big problem.

Risers also allow oxygen into the septic system, which causes all sorts of problems. If you’ve ever been around a properly-operating septic tank, you’ll notice there’s very little odor because the gas has no way to escape. With risers, however, they create perfect ventilation points for gases to escape from your system and enter your yard through the riser hole – creating stinky odors that will attract flies and mosquitoes if left unrepaired.

Unfortunately, this means that even if you try to fix an odor problem by placing mosquito dunks in the riser (which is ineffective), the problem will still remain since it’s coming from outside your system.

Because of this, using risers should be avoided at all costs – especially if you live in an area where mosquitoes are common. If you can’t avoid them completely, make sure they’re outfitted with very heavy-duty screw-on or solid covers that will prevent rainwater from entering your septic system through the riser hole.

Septic tank risers are another way to allow water into the leach field lines, which leads to overloading and rapidly filling tanks. In addition, soil can become saturated around the riser holes, which forces effluent out through the top of rip rap stones to seep into soil instead of being allowed to filter down vertically within the underlying rock. This, too, leads to overloading of septic systems as well as water pollution problems.

In addition, this can also cause the leach lines to collapse – either from poor soil drainage or from seepage of effluent up through the rock and out onto the surface. As a result, expensive repairs are often required for both problems if not immediately addressed after installation.

Septic tank risers should never be used where there is any possibility of human contact with your system’s effluent – especially if you have small children crawling around on the ground near riser holes because there is no telling what sort of disease could be transferred into their bodies from contact with effluent coming from these holes. It’s best to keep the riser holes completely covered with solid lids so that even if there is a problem and effluent does come out of them, the possibility of human contact is minimized.


Meet Jeff. For the last 10 years, he's been repairing and fixing problem homes - from leaky roofs to faulty wiring. He started blogging about his experiences as a way to help others who might be struggling with home repairs, and he's become something of an expert in the field. Jeff is always up for a challenge, and he loves sharing his tips and advice with others. When it comes to home repairs, Jeff knows what he's talking about. So if you're looking for some help and guidance, be sure to check out his latest guide!

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