I think you need to call a plumber. We got that a lot living in the Southern California Desert. But never in the laundry. Mostly in summers, if we didn't flush the toilets in our guest house, we would get that smell, and the fix was just to dump fresh water in the toilets, sinks and showers. Good luck. Be interesting to see how this turns out.

You might have two different problems going on.

That musty odor might be something growing inside your washing machine.
The sewer gas is toxic and dangerous. I'm having a hard time envisioning how the trap is not filling fast enough from the washer, since all the traps I have seen are on the sewer line for each device. Nonetheless, you need to get a plumber out there right away. Years ago, a sewer gas odor began in our upstairs. Long story short, the A/C condensation drain was routed thru the sewer gas vent piping (completely against building codes), mold & scum started growing over the years, to the point the gases were sucked back up into our HVAC ductwork, every time the A/C cycled on.

There shouldn't be sewer gas making its way to the washing machine. Sewer gas could enter through a floor drain, but that would indicate their is something wrong with the trap. Is your laundry up or down? How us the discharge tube connected, basin, standby pipe? You truly do need a plumber, but honestly the residual wAter left in the machine/pump would prevent such a thing. This is a first.

The sewer-gas-like smell might have come from the gunk in the drain hose, which is decomposed material.

Is this a front loader? Regardless an empty load with the hottest water possible and a cup of Clorox run on the longest cycle would certainly erradicate any mold or growth issues. The other possibility is a rogue sock or other piece stuck and has decomposed. I don't believe it's sewer gas simply because the drain hose is NOT part of the fixed household plumbing, or at least it shouldn't be.

The washer is a top loader, and is located in the basement of the house, or underground (1-story house w/finished basement). The drain hose that is connected to the discharge line of the washer leads up 3 1/2ft into a trap in the wall. I have never smelled the gas leaking into the house, only from inside the washer during a rinse cycle (when the water drains, and starts spin/rinsing). I'm not certain if the situation calls for a plumber, could be a complete waste of money. I already cleaned the drain hose, but perhaps it needs replaced altogether? Maybe the wall trap needs cleaned as well, but I'm not sure if it would make any difference, or if it would be possible to clean myself.

Perhaps i was a little more detailed than i should have been in the OP, but i wanted to paint the whole picture. I am mainly looking for ways to remove the musty smell from my laundry.

Musty to me equals mold somewhere. Please get a plumber or mold remediation company out there. Spending money on your health is priceless.

There could be a leak in your wall rotting the support beams which will not be a cheap fix. I think we are more worried about you than you are.

Yes you need a plumber without question!

It may not be what you want to hear, but I would have it checked by a professional as well. You can not be too cautious in a situation such as this.

As far as the smell in the clothes their are some things you can do to help that. Baking soda is useful, but in my experience, not up for heavy duty smells.

I would run a clean tub. You can use affresh tablets or bleach. For a lot of mold or just build up it may take a few clean tub cycles ( or the longest, hotest, extra water cycle you can run) to clean up the machine.

I have heard some people use a Lysol concentrate, in a brown bottle for laundry disinfecting and odors. I have not tried that though.

For odors in laundry I have had good success with oxygen bleach, borax, ammonia, and OdoBan.

Use the hottest water you can for the fabric, and along with a good quality detergent ( this does make a difference) just add in something for odors.

Odoban can be bought from home depot for $10 a gallon, and you just add in ½-1 cup. This has always worked for me.

Borax can be bought at target for $4, you can add ½-1 cup per load. You can also soak them in a borax/detergent solution, sometimes the extra time really helps with odors.

Oxygen bleach like oxiclean, oxymagic, etc. Also helps with odors as well.

My sister does her laundry at my house sometimes, she works in food service. Her clothes reek!!! After reading some posts here, I decided to try ammonia in her load of clothes, ½ cup. Works every time, no oil stains, no horrible smells, just clean fresh clothes. I never would have thought to use ammonia, it smells bad, but works. Just NEVER combine bleach and ammonia, or you literally risk your life.

Good luck, and let us know how everything works out.

Puddlepond, why put your health in danger by not having a professional look at the problem? Basements are not well ventilated and the gas will build up over time, after all where is it going to go. Dryer will exhaust the air but...

Smelling the gas after the first wash would lead me to believe you have a venting problem and that possibly your vent lines are clogged or improperly vented. Got the last one from "This Old House" where Rich the plumber explained why he had to move a vent point across a room to prevent improper venting drawing in waste pipe gas into the kitchen appliance and sink.

I had a similar problem which I was sure was sewer gases coming in somehow, but it turned out to be my washing machine. Try running a few hot water cycles with lots of bleach to see if that solves the problem.