Septic tank: Just noticed this today. What is it?

[morzh]

My wife alerted me today - it is a recent thing. My septic tank is covered with gravel and the border starts right at the walkway, extending inside the front lawn.
It seems like some sort of a pipe just got exposed from under the gravel. I am sure there should be something that covers it else gravel will keep falling in.

What is it and what am I to do about it?

Here are the photos.

The whole thing and the blow-up.

 

[Mr_David]

I would pull the rocks back and cover it. You really don't want rocks falling into it, what ever it is.
Could be a line clean out that someone forgot to cap.

 

[morzh]

Do I need to put a solid cap on it or a grating-type cap? I mean, if I just put gravel on it, it will keep falling in, but what I am not sure of is do I need to leave the way for the gases to escape or a solid cap is needed?
The line cleanout access is closer to the house and is capped above ground level.

 

[frodo]

it looks like a 4'' pipe. most likely a clean out
buy a clean out female adaptor and a threaded cap and install

 

[morzh]

it looks like a 4'' pipe. most likely a clean out
buy a clean out female adaptor and a threaded cap and install

Yes it is a 4" pipe. The cap has brome in half and the broken off piece fell in and so did the gravel it held.
I tempirarily put in a lid from large yogurt jar larger n diameter and covered with gavel, until I buy the adapter.

Q: is (was) the cap threaded or just smooth? What kind of adapter? Do I glue it or just push onto it, or screw?
Could you give me a link to an appropriate item fom some website?

Thanks,

Mike

 

[frodo]

if the pipe wall thickness is .120 it is SDR-35 pipe
if wall thickness is .237 it is sch 40 pvc pipe

https://www.lowes.com/pd/4-in-dia-PVC-Cap-Fitting/3133139

 

[morzh]

Thanks a bunch!