How do you get rid of a damp smell in A washing machine?

Try running a hot water full tub of with vinegar and a few old towel or stuff that is kinda soft through the longest cycle you have. then open the machine, remove the towels, and let the machine air dry. If this doesn't work, you might try running the tub full of hot water and adding some bleach and before it can drain shut it off and let that soak for about 20 minutes. then finish the cycle and air dry again. The smell is most likely coming from the outer tub that keeps the water in the tub. it is made of plastic usually and there could be some mildew in it you would never see unless you remove the inner tub. If you continue to have a problem you might want to consult a technician because you may have a leak that is letting water drip into the housing of the machine. If it is a front loader make sure the boot on the door is wiped out and free of mildew. There's also a product called Smelly Washer that should take out the smell.