Q. We have had an odor in our home for more than a year. In the winter, it is quite mild, but in the summer humidity, it is strong. It is the worst when we are coming in the house from the garage. When we enter the house, we step into a small hallway, with a bathroom on the right. The family room is at the end to the left. The home is a typical four-bedroom, 2½ bath. The best way I can describe the smell is sour. We have very little carpet, and the carpet in the family room is new.

Not sure whether the smell could be from the washing machine (a top loader, 8 eight years old) or the fireplace. We had a chimney sweep repair tiles; there was leaking (oil from the furnace). We don’t use the fireplace, and the chimney sweep checked, there were no dead animals in there. Any suggestions you have would be helpful. It is embarrassing when we have company.

ELAINE

A. Hi, Elaine. You mentioned the usual suspects. I’d search for the following:

Mold

Pay attention to lower areas along the garage walls and floor drains. Remove all old papers, boxes, and anything on the floor that is in contact with damp concrete; mold loves to live on these surfaces.

If you do find mold, clean with a disinfectant like Sporicidin, which is recommended for use in hospitals and medical, dental, and veterinary clinics. As an Occupational Safety and Health Administration-compliant disinfectant, it is ideal for cleaning and restoration work, such as black mold removal and water, fire, and sewage remediation. Sporicidin disinfectants kill 99.9 percent of mold, mildew, bacteria, and other odor-causing organisms that occur as a result of water and flood damage. I’m sure there are other cleaners out there, but I like using it on my projects, and get great results with it.

Washing machine

Some develop a musty, mildewy, sour-scented stench. You have a top-loader, so it might not be a problem. I’d still run a cycle of baking soda and vinegar (instructions below). Front loaders are efficient — they use very little water and require high-efficiency detergents — but too much or the wrong kinds of soap and softeners can cause rinsing issues. As a result, the washer drum ends up getting coated with a layer of soap scum, which invites mildew, bacteria, and mold. Front-loading washers also have a rubber door gasket to keep water from leaking out. Dirt, soap, and bits of fabric can get trapped under the gasket, creating nasty smells.

Not all front loaders are the same: On my washer there is also a drain trap filter pan that is accessed by removing the service panel. When I clean my washing machine, I also clean this drain trap. It usually is a trap for lint, coins, screws, and other things that fall from my pockets. It also gets pretty smelly.

Here’s one approach for cleaning:

I’ve tried running a cycle of bleach. It works but not as well as baking soda and vinegar. These two ingredients break up residue stuck to your drum and kill any mold that might be present. They’ll also help remove foul odors.

Mix ¼ cup baking soda with an equivalent amount of water. Add this solution to the machine’s detergent container.

Pour two cups of white vinegar into the empty drum, then run a normal cycle using hot water.

Scrub away any remaining grime. Don’t skip this step, especially at the rubber gasket. Remove stubborn spots with a kitchen scrubbing pad and a mixture of one part white vinegar and one part water.

Repeat once a month for maintenance.

Q. In my condo guest bathroom, a sewer odor is released when the sink faucet is turned on. Why would this occur in one bathroom but not the other, which is on the other side of the wall? I assume it may have something to do with the toilet drainage. Before I call a plumber, I would like to have some idea of what is entailed in addressing the problem.

HOLDING MY NOSE

A. Sounds like you may need to clean the bacteria-filled gunk and debris out of your sink’s drain and drain trap. I’m guessing that when the water hits this gunk, the bacteria smell rises up.

Rob Robillard is a general contractor, carpenter, editor of AConcordCarpenter.com, and principal of a carpentry and renovation business. Send your questions to homerepair@globe.com or tweet them to @robertrobillard.