septic system odor question

I have a question about the odors that come out of the vent pipe of a septic system.
I have a house that has a septic system. I had the septic tank pumped out two years ago when I first moved in. I have noticed that on some days, there is a slight sewage smell on the front of the house after a shower/flush/wash cycle. I have determined that the smell does not come from the septic tank or the drain field directly, but rather from the gases coming out of the vent pipe on the roof. These gases come down the roof to the front of the house. The house is on the less windy side of a mountain and is surrounded by trees.
My question is: Is this smell normal, or is it a sign of a problem with the septic tank? Looking around the web, I have found articles that say there shouldn't be an odor coming from the vent pipe, and other articles which say the smellis normal and can be minimized with a filter.
Thanks for any advice.
-David, snipped-for-privacy@yahoo.com
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The ventilator for your house's internal sewage pipes is called the Stack Vent. When working right, sewer gases move up in the atmosphere and you do not smell them. Certain weather conditions prevent this, so that the smell travels down to ground level. 1. This happens at this address about once a year for 2 to 7 days in winter. 2. The only cure appears to be an aerodynamic ventilator atop the stack vent (like factories use, to spin in the breeze and because of its shape suck gases out of the pipe.) But no such ventilator is made to fit stack vent dimensions (according to the roofers working here last week.)
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Don Phillipson
Carlsbad Springs (Ottawa, Canada)
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Try adding some additional pipe to the vent in order to discharge the gasses at a higher level so they will dissipate, the same principal as used in chimneys.

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The same thing happened to me. After having the septic tank cleaned again the smell disappeared. Mine is an aerobic, not sure if this makes any difference
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snipped-for-privacy@yahoo.com (David Martin) says...

I replaced my septic tank about three years ago, and suddenly was beset by septic gasses that would gag a maggot. It became very unpleasant to be outside in the yard. I tried various biological agents in the septic, to no good effect. Finally I just poured a gallon of vegetable oil down the drain to try to scum the surface. I noticed an immediate reduction in the stench, and this year I haven't smelled it at all.
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http://home.teleport.com/~larryc

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