I noticed it for the first time 4 days ago, when I would take a shower or run the dishwasher, flush the toilet the smell of diesel fuel takes over. You cannot smell the odor without water running into the drains, and we have taken the water into separate (hot/cold) containers and removed them from the home and the smell is not in the water. The smell is getting stronger and can be associated to diesel fuel or cat pee smell.

One guess: a dead animal in the drain, which smells similar to cat pee in my opinion (worse). You smell it when the traps are not full of water (when water is rushing down through them, but with enough air space to allow the smell back up). It may have fallen down a vent on the roof - bird, squirrel, mouse, but one one big enough to get trapped without causing a backup, often a bird because of the feathers both trapping the body but allowing water and air past.

If it were just one fixture that smelled when you drained I could buy into as drainage problem but that's what traps are for.

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when the traps are not full of water (when water is rushing down through them, but with enough air space to allow the smell back up).

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That's simply not true. If it were we'd be flooded with similar complaints. The trap has a "U" shaped bell that traps the water for a seal.
So that brings me back to your water. Are you on a well? Does the water smell coming out of the tap? Any floor drains that are not in use? Any other fixtures that you have that aren't being used? Just trying to cover all bases. n Cheers, Tom

I think my theory is plausible, unless the fixtures are all way far apart from each other. (Please say - are your kitchen and bath next to each other?) Traps are gurgling with air when water is actively flowing down them, so the smell of a dead animal can escape more easily, and this person's smell is getting worse, suggesting further decomposition, and soon even standing water in the traps will be smelling. As for the smell of cat pee, I have been told that the house I'm working on smells like cat pee but I know it's dead mice and mice droppings and mice urine. But a bigger animal is more likely to have fallen down a vent and lodge in the drain just enough to let water by without getting swept on down the line.

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Traps are gurgling with air when water is actively flowing down them,

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Thank you! You just made my point!
Traps do not "gurgle" unless there
S a blocked vent and the fixture's attempting to vent through the trap. The "gurgle" you hear is them air being drawn past then water seal. If your traps gurgle then you should have your own vents checked and cleared. Cheers, Tom

OK I defer to that.
I mean that explains why this person doesn't smell the smell unless water is going down the drain, at least for now. If he or she locates the vent(s) and can get to the place where the vent meets the waste pipe, isn't that the most likely spot to find a dead animal?
I hope Lisser12 answers your questions, speedball.
(My traps don't gurgle. My kitchen subfloor and wall cavities just reek where mice were.)

It's very seldom a critter get down in a vent and when they do they either go out the main or block the vent/drain.

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If he or she locates the vent(s) and can get to the place where the vent meets the waste pipe, isn't that the most likely spot to find a dead animal?

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No! To get in the drain from the vent he would have to navigate the branch of the sanitary tee. If he were small enough he would go straight past the drain into the branch that connects to the house main. More then likely she has odor coming from the trap raiser. There will be a small amount of air expelled from the raiser as she first starts to drain. I suggest taking a old bottle brush soaked in full strength bleach and scrubbing down the drain and raiser. Cheers, Tom