venting washer machine and utility tub properly

[fretless]

I am getting ready to replace my utility tub, and I would like to correct the plumbing problem while I do it. When the kitchen sink upstairs is running, the utility tub gurgles sometimes. The kitchen sink drains horizontally before dropping vertically to the basement where the washing machine and utility tub are located. They drain to the vertical pipe coming down from the kitchen, but there is no separate vent pipes for the washer or tub. I have attached a picture showing how it is now. How should I change it to avoid the gurgling?

[nukeman]

The tub and WM are not vented, so that is probably why you are getting the gurgling. The best fix is to run a separate vent up to the attic and out the roof (or you could tie the vent in 6" above the kitchen sink if there aren't fixtures from a higher level draining down). Running a new vent can be difficult and may requid repair work in you upper level(s). However, sometime you can run it in a corner of a closet and minimize the repairs.

The other option is an AAV (if allowed in your area). These are a mechanical device that lets air into the line, but not out. These need to be placed where they can be accessed (since they will need to be replaed down the road) and they also need to be able to breathe.

[fretless]

Thanks for replying. I'm amazed that they weren't vented. The house isn't that old. Looking at the picture, does it matter if the washing machine vent is above or below the backflow preventer?

[nukeman]

A lot of people get venting wrong. A plumber should have got it right, but you never know. No place that I know of allows wet venting between different levels (basically what you have). Could it be that the WM and tub were added after the house was built? I know that often in basements and such when plumbing is added, either:

1. venting is too hard, so they don't do it
2. they think that connecting into the stack within some distance is good enough to vent it.

In my house (built in '68), nothing in the basement bathroom or laundry was vented. I had similar issues. In my case, the trap in the shower would get the water pulled out of it and you would get sewer gases coming in. I had to cut concrete, re-work the plumbing, and run a vent from the basement to the attic and out the roof (which was a pain with 2 finished levels above the basement). Now, everything is good.

I'm not a plumber, but I would do the wet before the backflow preventer. In fact, I would probably remove the backflow preventer as it probably isn't doing anything for you. If you had a backup, it would just overfill the laundry tub. The problem with backflow preventers is they are mechanical and anything that may cause them to stick wll cause them not to function. It may not be as much of an issue on the WM or laundry tub line as a main line, but I suspect lint and such could cause it to stick. If you keep the backflow preventer, I would also add another on the laundry tub side.