This just started....when my Wife does laundry, we get a Septic Odor in the Laundry room. We bought the house last year, and this is the first time we have had this issue. The waste line for the Laundry has a trap, so it puzzles me how gasses can enter past the trap???....the odor only occurs when doing laundry....when she's done, we just air out the room and the odor disapates. The Septic was pumped just before we closed on the house almost 1 year to the day....it just doesn't make sense to me.....any ideas???

It sounds like you either don't have a vent on the washing machine drain, or it is vented improperly. If it is vented, make sure it is vented to the outside and not just stubbed up inside a wall somewhere.

Good luck!

there can be two reasons for this happening.

The trap is being pulled dry from a siphon action elsewhere in the drain line. There should be a vent pipe somewhere slightly downstream from the trap. This vent allows air to enter the pipe when lets say a toilet or sink drains fast. Air is needed to fill the void which is sort of a suction in the line. If the vent is plugged, Perhaps something covering the vent on the roof? The suction created by the large volume of water going down the drain pulls the water out of the trap that is connected to the washer.
Also a undersized trap for the washer could be the cause.

Other issues can cause this but without knowing where the laundry drain pipe is in relationship to the rest of the drain piping it would be hard to determine the cause.

Be sure that the pipe for the washer is loose within the drain pipe. If its not the water will not get enough air to properly drain and it can siphon the water out of the trap while the water is being pumped out of the washer.

I too, was thinking a venting problem.....maybe the Trap being sucked dry.....but wouldn't the odor always be there after the wash is done ???. It only happens while the wash is running....just air out the room and the odor disapates. I took some pictures of the Washroom Drain to show how it relates to whatever plumbing I could see in the crawl space.
...The Main Pipe is obviously leading out to the Septic......the Big Pipe to the right I belive is for both Bathrooms upstairs.....the middle pipe is for the Washroom on the other side of the wall....the pipe to the left I believe is for the Kitchen directly above.....where is the Vent????...dunno....probably part of the Bathroom plumbing in the walls above. This is the first time we've experienced this

If the main plumbing drain to the right is properly vented then you "should" be okay since it would allow the wash water to pull air from behind the flow, even though each fixture really should have its own vent even when they share a common main vent. Since the problem apparently started suddenly, it's possible that the main vent has become obstructed.

The trap will only do so much as far as preventing backflow of gases. When the waste water pushes down the pipe the pressure from the air being displaced will find its own way out if a proper outlet isn't provided; either that or the water will just stop draining due to the back pressure.