I know it is to give access to snaking out sewer pipe if there is a clog... but, my question is... does the cap need to be on to keep pressure in the line to prevent clogs? Is there a health hazzard if the cap only sits on the opening? Any info would be great!

You should keep it on there securely so no sewer gas makes it's way into your basement.

my question is... does the cap need to be on to keep pressure in the line to prevent clogs? Is there a health hazzard if the cap only sits on the opening? Any info would be great! The clean out cover is there primarily to give access to snake the line. The cover does not hold pressure but it does seal off any sewer gas that may escape and should be screwed in tight. Sewer gas is a health hazard and the methane content makes it explosive. Regards, Tom

Agree with all. When you drain something like a washer or bath tub there could be a cahnce of water momentarily coming out of the clean out in addition to the sewer gas issue.

The SCREW ON cap is very important to keep water/sewage from coming up in case there is a blockage beyond that point. Once upon a time my basement used to flood all the time whenever there is a clogged sewer trap. I had so much problem washing,disinfecting and cleaning each time it happened. My wife and I came up with the idea of changing the push-in cap to a screw on cap and it solved the problem.if there is ever a blockage it would have to show up some other place like at the main trap in the boiler room before,where it can be dealt with easier before flooding the whole basement.
I am assuming that this is a secondary trap and not the main trap. The main sewer trap I think should not be screw on.If there is a blockage that's where it should show up. I am not a plumber. Just my experience and opinion and observations.

By the way , I paid thousands to a so called plumber changing out all my main pipes that weren't so bad after all,and still endeded up with a flooded basement multiple afterwards. It was the idea of the screw-on cap at the secondary trap that solved the problem. I do have clogged drain since then but I would discover it early, before it flood the basement and I only have to clear it.

ALWITZB: this is a 2 year old post you are responding to...