We went away for a couple weeks and upon returning we opened the door to our home and noticed an odor that wasn't present before we left. I don't know exactly how to describe it, but it had almost a moldy, dead mouse odor. We searched high and low with no success and finally i decided to check all the drains in our home thinking something was going on. I got to the last one which of course is behind the furnace where the air conditioner condensate drains. I removed the grate and shined a light, all I could see was black moldy water. I started cleaning with a long handled brush and moved on to a drain snake. I hit the clog and instantly the entire basement smelled like a giant rotten egg. I kept snaking and pouring clean water down the drain. Once the water was clear i poured a mixture of baking soda and vinegar and the smell was gone. We have lived in the house for 20 years and it never came to my mind to clean that drain. We always had a slight musty smell and just attributed it to a basement being a basement. I wondered out loud if many times a clogged floor drain is the reason for odor and home owners think it's a project that requires waterproofing.