Water constantly in pin trap

As someone who has had a deep well drilled and found water, but water contaminated with iron and sulfur, I can tell you first hand about the rotten egg smell. The water softener will remove the iron that can turn clothes orange, but doesn't do anything to remove the rotten egg odor. You will need a charcoal (carbon) water filter to eliminate the sulfur smell.

The smell is sewer gas coming back in the house from the sewer or septic tank ether from a dried out water trap in a floor or fixture drain, or from the roof vent, or a hole or separation in pipe or fitting. Like wax ring under toilet. First pore water down every drain to fill any trap that might have gone dry, then flush toilet or run washer or drain bath tub.This will displace gas in pipe and will cause the smell to increases if there is no smell then the problem is fixed if not check roof vent it may need a charcoal filter on top, There is no water trap on air vent on roof and is an open hole to the sewer or septic, The heating system in the winter or AC in summer will draw the gas inside from the vent.If it is the vent you should be able to smell it from outside. If all tests fails You will need to have a smoke test done. A smoker is set up outside and the line is filled with smoke and will show where gas is coming from. Also it might be a good ideal to check all gas fittings in case it is a gas leak.

Check the drain where the wash machine is plumbed into it should have the blung to stop the smell comming out of the drain,also check the filter but it is very rare that the smell will come out of the washer it will be a drain issue that is backing up through the washer,if you havent got a u bend trap on the drain it will allow the drain gases to come back into the house.
hope that helps a little bit.
adrian

Hydrogen sulfide gas. Try pouring a quart (liter) of distilled white vinegar mixed with a quart (liter) of water down the drain. Let it stand for half an hour, then follow it down with several gallons of water.

If that doesn't clear it up, you may not have a trap - that's a health hazard, and you'll need to have one installed.

Any time you get a strong smell of rotten eggs it is due to a high concentration of sulfer in the water. Are you on well water? I would suggest using a cleaner like http://www.sani-bath.com/ to clean out your system.

Does the sewer drain line have a trap at the bottom that prevents sewer gas from entering the room? If the smell seems to be coming from the washer itself, run a wash cycle empty with a cup of baking soda, detergent and hot water to clean the interior.

Two different problems. Rotten egg smell is sulfer from the water supply, especially strong in heated water. Drain may need to be cabled out. 

its the mag rod in water heater-if your not using alot of hot water,and water is sitting in heater it will smell like rotten eggs-u can remove mag rod from water heater.it is in top of heater-

Make sure the rubber door gasket is clean. Pull it back and clean under and around it. The gasket will collect dirt and begin to mildew causing various odors. Run the machine empty, boil a medium pot of water to almost boiling, then put it in the machine during the wash cycle. This will help clean the lines, during the rinse cycle place a 1/2 cup of vinegar in the unit. Make sure you are using HE detergent. 1-2 tablespoons will due. If your using liquid fabric softner, dilute it by half. These machine use less water than a typical top loader and can't dissolve regular detergent effectively. There by causing your lines to get clogged with gunk.

Repair man told me this is common with front load washers. I was told to put Sunlight dish washing detergent (for dishwashers not hands) in the machine (about 1/2 cup) and do a hot wash with the machine empty.