I have an older house with a kitchen sink and wash machine that use the same drain. After washing clothes or dishes there is a nasty odor that comes from the basement. (I assume where the drain is) There seems to be no vent to the outside ? Does it need one? Does it have to go through the roof or can it go out the side of the house? Thanks for listening and would appreciate any help!!

Do you have a floor drain in the basement and have you poured water in the trap? ALL FIXTURES that are trapped are required to be vented. However they don't all have to exit separately. Sometimes we we tie them back,(revent) to one vent in the attic that we terminate out the roof.
Regards, tom

It sounds like you don't have a trap on the drain. This could be on each of the drains or one after the two drains join. ( The trap is the U-shaped section of pipe that should have water in it to trap odors.) The drain system should also be vented through the roof. ( you might notice odors if vented through the wall.) the vent shoud be branching off after the trap.

Thanks for the info. There is a trap after both drains but I did find a floor drain that was empty as wewll as an unused toilet that was dry. I added water to both and we'll see what happens next laundry or dishes day. How would you add a vent when the wall, ceilings etc. are all finished?

I thinkyou just located and taken care of your problem. I should have exempted floor drains when I said all fixtures that have traps need to be vented. Cheers. Tom