Smelly sink w/washing clothes

It is likely that the sewer pipe to the street from your house is getting plugged. Most household drain clogs are at the wash tubs in your basement. The tubs your washer dumps into. It clogs there cause when your washing machine is constantly dumping fibers from your closes after agitation down that drain. Watch for these. Seems to be draining fine until 4th or 5 load and then clogs. Drainage seems fine in morning but becomes clogging later in the day. If this is happening, your clog is far enough down the sewer drain that it allows some water to drain before it fills to the point of no longer draining. You can prevent this problem by going down to your hardware store and getting a "plug filter" for a few dollars to screen off some of those fibers and prevent them from getting in your drain. Now, If your drain is clogged it may need to be "snaked". If you call Roto - Rooter they can fix it for a cost of about $150. But consider trying this first. Go out and get 1 Gallon bottle of "acid" drain opener. You won't find it at your grocery store. You will have to get it at a hardware store or I have seen it at Home Depot. It's not Dranno or Plumber in a bottle stuff. Most places won't handle it cause of the libilities issue. CAUTION. I'm talkin about a potentially dangerous product. If you add COLD water to acid, it can erupt and cause severe burns to body. It is SULFERIC  Acid. Same stuff in car batteries. READ EVERY DIRECTION on the bottle. It comes in a Black bottle for about $12 a Gallon. You will need 1 Gallon and perhaps 2 is clog is really bad. It has a guarenty that it will work. I've used it several times and it always has. Being very careful, pour about 2/33 on the Gallon into your Basement floor drain. Best after the drain is clear of any water build up so it doesn't get diluted by water. Turn your head as a safety away from drain while pouring cleaner in drain. Careful of gasses be sure fresh ventilation. Leave it in drain for about 3 hours without adding more water. Then Flush the drain with WARM water. It is the best drain cleaner there is. After a few hours, put the remaining drain acid down your wash tub drain and again wait about 2 more hours flush again. You may consider a second application (Gallon) if drain is still clogged. Or, Buy a "Drain snake" at Home depot's" plumbing dept. for about $20 get a 50ft. snake. Do it yourself by ramming the snake down the same floor drain (remove drain cover first) look inside the drain with a flashlight and you will see the hole to ram the snake in. As you push the snake in farther and farther you will likely find where the clog is and keep pushing the snake intil you feel that you have broken through the clog. It's about $20 for a 50 or 100 ft. snake but you will likely use it again. A good household tool cause drains always get clogged. Do it yourself and save $150 - $200. And if you don't get a "filter washer strainer" to protect those washer tub drains. You will do it all again in 2 or 3 years.