We have a new home with private septic tank. All plumbing fixtures have vents except for kitchen island which has a gravity fitting on it that is supposed to fight odors escaping through the drain. We have had our plumbers come out several times regarding sewage smell. It started in the master bath... which was remedied by a new wax seal on the toilet. Once the master was fixed the smell started in the guest bath, same story, new seal fixed the problem. Now the smell is in the laundry room, kitchen island, and worst of all the powder room. The plumber has no idea on the laundry room. The island he thinks is the gravity device that we are changing this week, as far as the powder room... its horendious!! They have changed the wax seal, and used silocone around the sink and toilet. The smell persists... usually at night. Our pipes under the sink are exposed and the wall flange does not fit snug to the wall. I have asked if this could be the problem and they say no. All sinks and drains are used regularly. Could one of the vents been punctured during construction? Also why is it so strong at night?
Please if you have any idea let me know... I'm very frustrated and our plumber seems to be clueless (they did all the rough in plumbing in the house)

I would check the venting. If this has been a problem from day 1, check the roof vent and see if they remembered to remove the test cap(s). By leaving those caps in place the sewer gas has no place to go but up through the p-traps and toilets.

:eek: Several supersize room fresheners in every room in the house or build some outside port a potties. :D

Good thinking but we don't cap off the roof vents. They are left open and we fill the system through them for inspection.
GOOSE, The smell's worse at night because the air's heavier at night and the odor drifts closer to ground level. Look down the drain at all the traps. If they're full of water then you should be OK, but if there's almost no water in any of the traps then you could have a vent that's blocked. Also you've tried everything else you might want to consider replacing the wax rings in your toilets. Sewer gas can escape a defective ring yet not leak water when flushed. The wax ring can emit sewer gases from the base of your toilets and you will swear it's coming from the shower/tub drain, lavatory drain etc.
Sewer gases have a way of dulling the olfactory nerve and make detection nasally impossible.
You must realize that smells and weird noises are the hardest to track down when you're on site and just about impossible when you're not.
All I can do is point out likely spots. Regards, Tom