strange smell--faulty p-trap?


Alright I've dealt with a recurring bad smell for about 2 years now, and after multiple visits from the plumber (unfortunately the smell was never around when they came) and multiple posts on usenet (the answers to which have tended to be a lot more informative than what the plumber told me), I think I've narrowed down the problem to the p-trap that's connected to my central AC drainage pipe.
The smell used to come when I ran the water in the kitchen. I got the p-trap cleaned out (it was VERY clogged), and the plumber added a t-joint kind of thing with a cap so I can occasionally pour bleach in to keep it clean. Strangely, the smell doesn't come when I run the kitchen water anymore, but now it just comes around randomly, usually near the end of the day. Not a pleasant thing to come home to after work.
I -think-, but I'm not sure, that the p-trap is either vacating due to some weird pressure thing in the plumbing, or just not filling as fast as it evaporates. Could someone more knowledgeable than me tell me if either of these make any sense? I've occasionally been putting water into that cap thing he installed, but it hasn't made much of a difference.
When I do a search for "p-trap" on google images all the ones that show up have a much steeper angle than the one that I have installed. I had foolishly not requested that the plumber put a new one in (I asked him whether he would replace it, he said he'd just clean it out which would save me money). Is this a possible problem?
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Possibly he needed to snake out the vent associated with this trap.
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Any smell is because your trap is not quite full and is allowing smell thru if your vent is good then look for leaks on your trap or a pluged vent Sev wrote:

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Sev wrote:

That would be the vent pipe that comes out on the roof? Or is there some other part of the system that I don't know about?
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I"ve seen old black iron and galvanized pipe used in vents rotted clean through and stinking up the place. You could easily have a leaky vent. snipped-for-privacy@hotmail.com wrote:

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if the ac unit drains into the kitchen sink trap itself where you smell it, perhaps it could have its own trap closer to the soil stack. a guess: you are describing a time of day related to the operating of the air conditioning creating waste moisture. moisture feeds the mold. have your moisture gathering ac unit and the drain line to its trap cleaned or snaked and bleached? maybe replace the drain hose/pipe from ac to trap? call your ac repairman out to look over your system layout and advise you of how to perform periodic servicing for your particular equipment layout. improperly vented systems can lead to trap being sucked out by other usage of your home sewer system. changing a working trap will probably provide no improvement in the problem since it sounds like mold odor creeping down the ac drain hose to the trap. systems and their installations and climates and local code requirements vary widely so a visit by an hvac technician should solve this.
snipped-for-privacy@hotmail.com wrote:

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buffalobill wrote:

I haven't snaked but I've poured plenty of bleach down the relevant pipe.

I think this is the problem, is there any way to fix this? I don't think it's mold, it has a definite sewer smell rather than mold.
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