My basement is plumbed but not finished. When using higher flows of water in the upstairs of my house (dishwasher, Laundry machine) I start to get a sewer odour in my basement. What I'm hoping it is, after checking all the drains in the basement, is my toilet drain. It has a plastic cap. But I'm hoping the odour is coming from there slowly leaking through the cap and collecting in the basement, and hoping that the problem will be cured once the toilet and sink, shower etc are installed. Does this sound right?

Sorry, I should add that it is a septic system. If that helps at all

Make sure all drains that are not hooked up in the basement are completely sealed until fixtures are installed. There should be absolutely no open pipes or you will get sewer gas.

Thanks, I will try buying a new drain cap on the toilet drain in the basement. It's the only one I haven't replaced since I moved in.

Thanks, I will try buying a new drain cap on the toilet drain in the basement. It's the only one I haven't replaced since i moved in.

Sounds like you've already located the source of your stinky. That open pipe left a direct open connection between your home and then city sewer. Good luck, Tom

I bought and installed a new flex cap drain cover over the 3" toilet drain. But I still have an odour every so often in the basement. The only other thing I can think of is, since there is no p-trap in the eventual sink drain, that odour is coming up through the vent attached to the sink drain line and there may be a leak in the vent line, on the way up out of the basement to the outside vent. Does this sound possible? And how can I fix it? Just run a layer of pipe glue/compound around the circumfrence of the joints? Or completely disassemble and install a new vent line?