First post, I did a quick search but didn't see exactly my situation here. Professional plumbers have helped us replace the kitchen and, directly behind it, our 3-in-a-row bathroom. Relocated the 40-gal AC hot water to be closer. Actually 3 different plumbers to get to that point. That was all working sort of OK, with occasional toilet blocks if dishwasher and kitchen sink were all draining at once, or if tub stopper was closed.

Last week we remodeled the second bathroom...this is a single-level 1958 home. Second bathroom shower/sink/toilet are perfect, and since all 3 were relocated they made a new through-roof vent. BUT, the toilet in the first bathroom is not draining. Gets clogged, pipes make noises for a day, then it fixes itself for a couple of flushes, then blocks again. Vigorous plunging with beehive just pumps a lot of air around, doesn't clear the bowl.

I can send diagrams, photos, more description of my two roof vents, etc. If there is already a write-up on venting that I should read, please send me a link. I didn't do any of the work myself, but if I hire plumber number 5 to fix this I would like to tell them what the problem is, and what is the recommended way to rejig things. Thanks.

We would need an 'EXACT" drawing of the system to even guess what the problem is, but does sound like a venting issue.

OK. Flat 2D drawings are not great for drain diagrams, but if you can access this image you may help me understand my flushing problems.
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on the 2023 remodel you need to REconnect the old vent AND keep the new one


you may use an AAV if you can not reconnect


if the AAV is in a wall you need a louvered access panel for it

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

No AAVs here. Previous vent was 3.5" PVC, located outside. What's the smallest I can use to replace it? I noticed plumber #4 used 2" inside the remodel wall.

This might not be the complete solution to my flushing problem. Remodel plumber put a removable cap where the disconnected vent was, I just removed it as a test and I still have very slow draining from the oldest toilet.

I will try to get a 5th plumber with a snake tomorrow or Tuesday, in case I have some stuck debris in addition to weird vents.



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I would also recommend they do a video inspection I’ll bet there is construction debris in the drain

I remodeled a 1/2 bath a few years ago and wound up with a double trap on the toilet. Of course the toilet has a trap built in but there was an unvented whole house trap that acted like a second trap added on the drain line and it made the toilet behave exactly like this. What seemed like a clog was actually air bound between the two traps, even though there was a vent connection to the pipe between the toilet and the external trap. Toilet would flush great for x flushes, then it would act like it was clogged. What tipped me off to the problem was that it started acting clogged when no solid waste was flushed.

May not be your exact problem, but some photos and/or better diagrams will help the pros here spot the problem.

Including toilets I have 11 traps. I really have 3 vents, because I've opened my test cap where the '74 bathroom vent used to be. I have lots of gurgle noises and slow draining now, since the 2021 toilet partly cleared itself at 1am Monday morning (woke me up) Plumber #1 said he would try to come with a snake today.

While I'm waiting I've corrected and added detail and photos for the pros to examine. Some things will jump out.

First, photo 1. Plumber #4 asked me before he cut through the floor joist for the 2023 toilet. Let's assume I didn't want the fixture in the middle of the room. What would be the optimal solution? Should I screw blocks into the joist to sister it, around the drain?

Second, same area. There is not a lot of fall from the shower trap to the side wall to the wye to the wye. But I don't think that's part of my flush problem.

Third, when you flush 2023, air needs to vent in from the roof to the sink to the wye to the wye. Is that an OK design or problematic?

Photo 2, no change to flush problems when this is open or closed

Photo 3. What's interesting is the ADU toilet has never backed up until this month, coincidently when workers were using it, and when the 2023 bathroom plumbing was altered, and when I beehived a ton of air into the system trying to get 2021 to flush. Waste actually overflowed here this past week, 70 feet from the main house.

Photo 4. Before and after the 2021 rennovation this toilet was never perfect, getting stuck every few months. It would clear with a plunger. But now it won't pass clear water except once every few days.

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the 2021 toilet is NOT properly vented

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

I believe you. What would be a good remedy? And thank you, I really appreciate all the replies.

installation of a proper vent - how we do not know w/o actually seeing the structure

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

Not a pro but your tub, sink, kitchen drain are vented from the toilet, but the toilet is not vented from any of them.

The tub is not vented when the kitchen drains, and the kitchen is not vented when the tub drains.

In the one picture on the far right, you have a sink draining into a stack to it's right, then the drain continues on to the left. That fixture is not vented. Should have two horizontal trap arms connecting to the stack.

Not sure it's a good idea to drain the kitchen past a bathroom group like that. The dishwasher has a pump and a garbage disposer create positive pressure. I bet if you fill up your kitchen sink remove plug then turn on disposer it will siphon water out of your tub trap. If you run the tub as well your toilet won't flush well.

Really difficult to advise since so much has been done, because not only the topology (how things are connected in what order) matters, distances between them matter, The only way I can see you get good advise is to show ISO diagrams for each group and try to see getting this examined and corrected.

This didn't pass inspection right?

???? INSPECTION, WHAT INSPECTION ????

The 'contractor' said he did not need a permit BUT never told me that I DID.

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"Measure Twice & Cut Once" - Retired U.A. Local 1 & 638

I hate it when readers are left hanging without a resolution, so here's my update: I have 3 flushing toilets, for the moment. This cost me $427 for 1.5 hours of snaking, no parts. In Key West, FL, good tradespeople are *expensive*

There was a tough obstruction about 10 feet from the end of the 1958 cast iron lateral. The spearhead and some swearing got things moving. That's not the end of the story, so keep reading if you're interested.

Imagine that if your daily "output" was low enough, waste could back up in the lines and then dribble through during the night, ready to go again in the morning. Imagine three bathroom-construction and tiler guys show up, start using the extra toilet out back, possibly putting things down there they should not, and your capacity is exceeded. Your lines would back up until the lowest drain, say the shower drain in my ADU, starts overflowing with sewage.

This is just one theory that fits the symptoms we had. There is no question I have insufficient venting, everyone in the forum and on-site says it could be improved. When was this last inspected? Before I purchased, my inspector wrote that the cast iron under the house was in poor condition and should be professionally replaced. After purchasing, I engaged a plumbing company to do this, at no small expense.

Previously the original toilet flush pipe hooked 16" back into the stack vent, below the combined kit-sink/vanity wet vent. Flushing was usually fine, even though we lacked a branch vent above the sinks. But my guess is that as soon as we replaced the rusted, leaky, overflowing cast iron under the house, we would occasionally hit "capacity" and have flush problems.

The new 2021 PVC then introduced additional issues: with no direct flush vent, it was harder than ever to clear clogs. If the main line is clogged, it's hard work trying to plunge it. Air can't easily flow from the stack, to the main line, across to the toilet and then up again. If it causes problems again, I will have a cross vent installed between the stack and flush pipe, kinda like it used to be. Plus the horizontal trap arms that were suggested by SUM.

And, for good luck, I'll put an AAV where the old bath 2 vent used to be. There was no inspection after the 2021 PVC work because of the added expense. I would have new work inspected, in case that brings me extra good luck.

One of the things you get with expensive plumbers is local knowledge. Initially we assumed that the dry city cleanout was due to the clogged lateral, or a collapse in it, tree root issues, etc. My cleanout is 6 inches from my neighbor's on the sidewalk. You can see where this is going. I flush, it comes through his cleanout.

The local plumbers tell me when the sewers were put into this area in 2001, some connections failed their pressure test. Rather than dig another, the city joined you to your neighbor and you were none the wiser. Arghhhhh. My neighbor is elderly and lives alone, so I'm causing more problems than he is.

Where does that leave me?

If problems with toilet 1, add vents as above.

If problems with multiple toilets, get out the checkbook. I'm guessing six grand to hoe in PVC to replace the lateral, and hook it into my unused city cleanout.

I really appreciate the suggestions here, and the time you guys spent writing back. Thanks.

Thanks for follow up.