I have two drains, a bathroom drain and a kitchen drain. Earlier this year my uncle and I had to tie the furnace drain into one of the main drains. Where the furnace drain was lead to, it got closed up years ago. So we installed it into the closest one, the kitchen drain. That worked for a while, but later on the furnace broke down ( Still is currently ). Note: The furnace has had water in it since we moved in, because of the furnace water backing up onto the floor. So after we installed the drain and the furnace breaks down, lately the house will start smelling like sewage when the shower is ran. The water is also backing up through the Y ( Where the two drains meet in the ground ) into the furnace. The water is going through the A coil and down into the bottom of the furnace. I took the panels off the furnace to see the water. The water was dirty. The sewage smell is also coming up through the drain in the basement floor. ( We have clogged that drain with a rag ). Is this linked to the age of the house too? The house was built in the 1950's.

Have you augered the floor drain? Sounds like the main drain is clogged.

No not that I know of, I am 14 so I am asking my parents most of the things. I thought maybe the bathroom drain is clogged. We did the Bleach solution that plumbers recommend but the smell still comes back. Could the clog interfere with the trap? There is also little white-ish dots in the water on the floor.