Floor drain without cleanout plug, yet no smell

Here's my garage floor drain that I have never looked at, until today.


I was cleaning the garage and all the sawdust etc. I had some rubber mats over the drain for months and noticed it was dry. So I removed the strainer and decided to really get in there and clear all the debris. There was some pretty caked stuff in there but I got it mostly out with the shopvac. It took a while to notice that the cleanout plug was missing, which is when I stopped. I'm no plumbing expert but felt like I knew how a floor drain works. Why have I not smelled any sewer gases in the garage during the several years I've lived here? Most of the time I haven't covered the drain. I'm guessing the cleanout plug doesn't just evaporate one day? I confirmed that this drain is connected to the main sewer line by flushing a toilet. I can clearly hear water running.

My theory is that the sewer gases have a lower resistance path going up toward the main stack so nothing noticeable comes into the garage. In case it helps the diagnosis: the garage is the last area the sewer line runs through before exiting the house. I've never dug it out but there's a big cleanout plug in the floor just before the garage door and I'm pretty sure of this.

Where do I find an expanding plug for this? Any other things I should check? I went to the local hardware store and only found a 1 1/2" test plug but this seems to be closer to 1 3/4 since it didn't tighten snugly. It certainly doesn't look like a 2" hole, which was the next size they had.

 

Well, as you've figured out, just because you have an open sewer connection, doesn't mean that it will smell, but it's good that you're going to plug it anyway.

They do sell inflatable test plugs, but I don't think it's a good long-term solution. Were you able to clean out the drain too?

 

To me that image looks like a floor drain with a side inlet for some other fixture, one that may have been abandoned. If it's a very old house, there might have been a floor sink that would drain in that manner. I'm not sure how you would use it as a clean-out.

 

Steve, I think the drain with cleanout looks basically like this:

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It includes the trap, and the cleanout bypasses the trap to make snaking easier.

 

Thanks Zorfdt,

I've never come across that configuration. Live & learn.

 

Thanks for the replies. I believe the main issue is solved. Here's the latest situation:

I went back to the hardware store and found a more senior associate who immediately walked me to the marine section, where I found the 1 3/4" plug. It was actually pretty tight to get in there but I got it with a rubber mallet. I then proceeded to continue cleaning the actual trap. It was pretty full of crap, including the original cleanout plug that had fallen into the trap. I got it out with the shopvac. I might try to get it in there but the threads are pretty rusty and full of stuff.

I had to get the snake out to clean the trap and found some film-like material that was stuck in the trap. I should probably still remove the plug and also clean the cleanout-side to make sure everything is free of obstructions. At least water now flows quite well.

The house was built in 1956. I removed another floor drain during a basement remodel and it had a backflow prevention ball in it. I would imagine this one did as well. Is there a chance it's somehow stuck in the trap? Since my modern floor drains don't have one, it probably doesn't serve any purpose to get one in this drain either? I also live pretty much on the top of a hill so the likelihood of me being the first one to have an issue is pretty slim.

The previous owners of this house have certainly not been the most conscientious homeowners. I have redone enough to know that plumbing, electrical, HVAC, and probably other areas have been neglected by either not cleaning/maintaining equipment, or doing a "remodel" with very sloppy workmanship. Probably not unheard of.

 

I think part of the reason I didn't realize it was a cleanout is that it would never occur to me to bypass the trap if I was snaking a drain. That's where the problem often is. Once you're through it, going forward isn't much more difficult.

Note that most modern traps are easy to snake through. The (much) older durham traps were hard to get a snake through.