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My house has both septic venting that goes up through the roof and also a vent in the yard. What is the need for the yard vent? Is this vent a requirement (code or otherwise)? A "best practice"? Or ... ?

Here's a photo of the vent when it was installed, just to clearly show the relationship to the house outlet (right), trap (center), and tank (left):

enter image description here

This came up because we are looking into relocating it, being in the way of a deck project.

The roof vent is standard, with all the fixtures passing through traps and then draining down eventually through the basement as well as venting upwards.

The yard vent sticks up out of the grass about 16' from the house. It is just upstream of an underground trap which feeds directly into the septic tank. (This is not a municipal sewer.)

At one point due to some project I had temporarily replaced the yard vent cap with a solid cap so there was no airflow, and noticed no difference on any plumbing in the house. (Maybe there could have be some long term effect we'd eventually have noticed?)

In reading around this subject I'm not finding yet anything reliable or pertinent for my system. There are discussions of venting the leach field or the septic tank itself, but my vent is neither of these. Being upstream of a trap I believe it provides at most pressure equalization as air won't flow through the trap by design.

I've noticed that some homes have these vents, others do not, that's part of the motivation for the question, to understand the reasons for the differences.

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    Any plumbing system requires vents at reasonable intervals. Also, the drain network in your home and the septic system are largely considered separate systems. Why you think that one should vent the other?
    – isherwood
    Jun 11, 2020 at 14:44
  • @isherwood why assume one vents the other... only because many houses seem to work that way. Is that possibly an out-of-date methodology? Also as noted in the Q, as far as I can tell this is not a septic tank vent, its just another vent on the drain line. (There is no vent of the septic tank or anything downstream)
    – StayOnTarget
    Jun 11, 2020 at 14:47
  • I haven't seen that. Every septic system I've been acquainted with has vents along the line, and of course the house will. I'm not a septic system expert, though. Just feeling for info.
    – isherwood
    Jun 11, 2020 at 14:48
  • @isherwood interesting... maybe the cases without it where I've seen that were the exceptions.
    – StayOnTarget
    Jun 11, 2020 at 14:49
  • It's hard to tell because that pic is a bit small and blurry - is there actually an opening at the top of that pipe, or is it a screw on cap? If it's a screw on, then it's simply a clean out. If it's open or has an AAV on it, then it would be a vent.
    – FreeMan
    May 20, 2021 at 11:15

3 Answers 3

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These are different things. The vent stack inside the house is there to prevent sewer gas from pushing back into the traps (as well as providing overall pressure relief). The vent in the yard is there to handle gas generated inside the septic tank. Whether that is required by local code, or as part of your specific design, or just because some people think it lengthens the tank and leaching field's life expectancy, I cannot say for sure. I have lived in towns where some people have added a tank vent, others have not, and there's no apparent rhyme or reason.

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  • @That distinction makes sense. In my case the buried trap is in between the yard vent and the tank. So I didn't think this was venting the actual tank.
    – StayOnTarget
    Jun 11, 2020 at 18:12
  • I added a photo just to show what I'm talking about. Could be my description is not clear or accurate.
    – StayOnTarget
    Jun 11, 2020 at 18:15
  • @UuDdLrLrSs Is your concern that in the photo the vent is on the house side of trap and not the tank side of the trap? I do not know enough about septic systems to answer but i would also like to know why this is set up that way.
    – Alaska Man
    Jul 11, 2020 at 20:18
  • @AlaskaMan yes that's it exactly...
    – StayOnTarget
    Jul 12, 2020 at 11:53
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So this popped up again - evidently I missed it the first time around. You have that vent specifically because you have that (not a standard feature) trap in the line to septic tank. That trap needs to be vented.

Most tanks that I've worked with, including my own, are vented via the vent through the roof at the house. A "whole house trap" is a deprecated idea I'm surprised to see installed in what appears to be a fairly new system. But having a trap there triggers the need to have a vent for it.

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  • But since I also have a roof vent, doesn't that make the trap vent redundant? Both vents are the same side of the trap.
    – StayOnTarget
    Oct 11, 2022 at 20:27
  • "doesn't that make the trap vent redundant?", No. The vent has to be installed in such a way to properly serve its purpose. A roof vent is too far away to be effective here.
    – longneck
    Oct 11, 2022 at 23:01
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This is an access point for a plumber to remove a clog in your plumbing system.

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    Welcome to Home Improvement. That "access point" is usually called a "clean out", and they're usually not right before a trap, since the trap makes it difficult to get the snake/augur through. Also, this was flagged as "low quality" since it's so short. Please take the tour and read through the help center, especially the part on answering, so you'll know how to best participate here. Sometimes a few words is all it takes, but, in general, a single, short sentence is not the kind of answer we're looking for.
    – FreeMan
    May 20, 2021 at 11:13
  • Its definitely a vent, since it has vent holes, although it is also a screw-on cap so it could be removed for cleanout purposes, maybe better than nothing even if its not an ideal location for a cleanout.
    – StayOnTarget
    May 20, 2021 at 13:35

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