We have been living in the same Condominium Complex for 9 years. We just rent our unit. Our building has 8 units in it. We are in a lower unit on a slab.
Since March this year, we have been getting a bad smell coming from the laundry room when we put the wet clothes from the washer into our dryer. It begins about 15 or 20 minutes after we start the cycle. We have torn apart the old dryer and washer and cleaned the whole length of the dryer vent. Still a smell

We ended up buying a new washer and dryer and still get the smell. It has been 6 months now dealing with this. Property Manager is trying to pass the buck.
We have gone through a process of elimination and have come to the conclusion that it has to be coming from the stink pipe which runs side by side in the same wall cavity. The dryer vent has some leaks as we have opened up the wall in a small area and you can see cob webs blowing around when the dryer is running.

In the laundry room, there is the water heater, furnace/air conditioner, water softner, washer and dryer. Water heater and Furnace (Gas) Washer and Dryer
Electric.

We have taken a vent and attached it to the back of the dryer and out the window and do not get a smell. Hook it back up to the vent and get the smell.
We are told not to shut the door to the laundry room because of possibly cutting off the air supply to the furnace... There is a definite problem with the return air.

What do you think the problem could be? Could it be a leak in the stink pipe and when the dryer runs the negative pressure is focing the air that is being leaked out of the pipe back down into our unit like a reversing of a vacuum?

I would appreciate any help.
Oh, there is water in the drain in the floor.. Not that.. Even sealed up the drain in the floor and the wall and still get the smell.

Thank you
Washer is a Top Loader LG, Dryer LG also... Not coming from washer, Dryer doesn't smell, clothes do not smell, air coming out of dryer vent outside smells like fabric softner... Something is blowing back in the room when dryer comes on, has to be something in the wall...

This seems like a most perplexing situation. Does your sink have a trap on the bottom of the drain? If it does then the odor is most likely not coming from the sink drain itself. It is possible that the sink drain pipe may have a leak, but it really doesn't explain why you can only smell the odor when the dryer is running. I don't think that the pressure from the dryer could cause this. I'm leaning more towards the odor being "heat activated" in a sense. If it were pressure related one would think that the odor wouldn't be delayed by as much as 15 to 20 minutes.

If you ever figure it out be sure to let us know, I'm curious now!

Our neighbors toilet had leaked about 4 years ago.. It was not just leaking water if you know what I mean. We noticed a bubbling in the ceiling of our bathroom. She replace her toilet and it was not seated properly and anything that was in the bowl was in the wall. It was fixed, but not cleaned up inside the common wall. It was left in there to stew..
The dryer vent runs through this area. After cleaning out our dryer vent after 9 years of living here (we were told by the association that the vent was cleaned regularly). We got about a 5 gallon shop vac full of lint out. The smell became more intense after this.
After eliminating everything else. Having the wall cut open exposing the dryer vent, we noticed that when we turned on the dryer air was leaking out of the vent in the wall that was cut open as you could see the cob webs blowing around. If the vent was leaking there, then it must be leaking in the wall all that hot air... The heat from the dryer vent and the warm moist air reactivated the said material that is in that cavity and blowing the stench back in through any crack or crevise it can back into our condo. The reason why we were not smelling it before was because the lint was insulating the vent and no air was able to escape into the cavity and the vent couldn't heat up.
We borrowed an inspection snake camera with a video and taped what was in the space and it is not pretty. It is pretty nasty...
We asked a restoration company if they could stop by and look at what we found and they agreed and confirmed my suspisions. It needs to be cleaned up pronto.
Still waiting to hear from the Association, Neighbor and Landlord about what if anything is going to be done.. They are fighting on who is responsible, so instead of smelling the stench, we bought a 20 ft flexible dryer vent hose and hooked it to the dryer and are venting out to our back window screen to dry the clothes. No smell that way... Can only do this for a short time because it is getting cold out. I guess the smell is re activated by heat and moisture.