AboutSharon McCarthy Expertise I can help with most questions about residential plumbing problems including septic systems, and some questions about irrigation. I have no experience with commercial installations or codes.
Experience I have been a sole-proprietor service plumber in two small towns north of Phoenix Arizona for 26 years.
Publications I had a monthly column in the United Steelworkers of America, local 1033, newsletter 1978 to 1982. I wrote an article for "The Theosophist" in 1977. I've written dozens of letters to the editor in many newspapers.
Education/Credentials High school and three years of college. My step-father, having worked 40 years in the plumbing trade in Chicago, taught me for two years. The rest has been hands-on experience.
Past/Present Clients Many hundreds of good people in Cave Creek and Carefree Arizona
Question I live in a double wide. The washing machine is on the other side of the wall from the toilet. When the washing machine drains, the water in toilet draws down and then on occasion bubbles up significantly. Nothing ever overflows.
I checked the main line to sewer and it is clear with no standing water. Put hose in vent on roof and ran water. Vent seems to be clear. I went in wall and just above the place were the water from the washer goes in the drain pipe is a mechanical vent cap. I replaced it. Still does it. I removed the cap and ran the washing machine without it. Still seems to draw the water down, but not quite as bad.
I am at a loss? I know it should be a venting problem. Nothing else is having the problem including garden tub or shower.
Jeff
Answer Dear Jeff,
What is causing this depends on: 1. Did this just start recently? 2. Has it been happening all along since you've lived in this house? or 3. Did you possibly put a new washing machine in?
A washing machine pumps something like 30 gallons of water out from a full load at a very rapid rate. Having this water gushing out so close to the toilet could possibly fill the 3" pipe so completely that there is no air gap to allow the venting process to keep it going smoothly.
It's not the vent going up that's causing this. For water to flow freely there needs to be an air gap even in the pipe going out. Like if you dunked a straw into a glass of water and put your finger over the top. Pull it up, the water stays in. Take your finger off, the water goes down. Same principle.
If you bought a newer model washing machine, it may be pumping water out faster and filling the pipe so full there is no air gap. If this has been going on all along, it's just a matter of the water pumping out so close to the toilet, and when the pipe fills completely it causes a bubbling back into the bowl.
If you are using the same washing machine, and this problem just began recently, then I'd say there may be a partial blockage in the line leaving the toilet; not enough to restrict a flush, but enough to slow the flow from the pumping of all that water.
