This Old House - How to Diagnose Plumbing Drain Problems | Ask This Old House

How long you guys been here? About 30 years. Right. And lately, in the last few months, we've noticed a smell, sewer smell coming from this bathroom. Okay. Is it all the time? No, it's not. Okay. Not too bad right now. No. We've noticed that the smell occurs whenever we use one of the fixtures upstairs. Okay. And then we also notice that in the toilet, the water moves when we flush upstairs or use the shower. All right. Can you do me a favor? Can you run up and just go flush the upstairs toilet for me? Oh yeah. Well, did you see it? Absolutely. That water level bounced when you flushed the toilet, and it really shouldn't. Anytime I see that, it suggests something to do with the venting system. The air inside that pipe is not getting out through the roof. Well, that's what we thought. We called a plumber who came over and put a camera down our vent. Okay. So, that's right down here. Yes. To the right. Okay. So, we are right behind the bathroom, and here is your drain, waste, and vent system for the whole house. Got a clean-out right here. The drain line probably goes underneath the bathroom and out the back of the building. Now, you can see right here. Here's where the water comes from the lavatory right behind us. The toilet comes into here. But at this point, this pipe right here, this full-size pipe, goes out through the top of the roof and acts as a vent to let the sewer gases come and go. A lot of times we find that animals get up into the top of it. The methane makes them die, they fall down in, and then they clog the vent. Now, did they run the drain camera down? Yes, they did. And they didn't find anything, of course. All right. So, what else did they check? The next step was to remove this cap and put the camera down this drain. And what did they find? They found that 22 feet away there was a water accumulation. Now, there shouldn't be any water in a drain line. Think about it. That drain line goes out like this with pitch. There shouldn't be any water except at the moments when you're running water or flushing something. So they found water. You found water. So where does 22 feet take us? Up here into the far corner. Look at you. You've been busy. You've been digging. I have been digging. There's an access door here, and I removed that and broke through the concrete. Yeah. And started to dig, and this is what I found. Now, that's not what I would expect. I would have thought the line would leave and go out to the street, or this way or that way, but it doesn't. It actually turns upwards. It doesn't really go too far, does it? It must go out, maybe an old downspout line. Let me go grab my camera and see if we can figure out this thing. All right, Rich. Here is a sort of drain snake, except it doesn't have a clean-out at the end. It actually has a camera and a light. You can see me. Let's see what the previous guy saw. So, we're going to go down through the drain. Now, I'm down in the horizontal. Oh, look at that. You see that? There's water in the pipe. Shouldn't be water there. We're underwater now. We're going 10 feet. It starts to get less water. That's weird. Okay. So, let's keep going out. All right. As we get out a little ways here, look at this. The pipe takes a turn. You see it no longer goes straight. If I was seeing a stoppage, I'd expect to see tree roots or some sort of thing. But this doesn't. This actually dives downward, and there's standing water right there. I think I know what this might be. Rich, I made a mockup out of PVC of what I think might exist underneath us somewhere right here. It would be cast iron, but this is the PVC version. Our camera is sitting at a place right about here, I think. Right below it is a thing called a house trap. The house trap is filled with water from here to this point. They're also called rat traps because back when you had a cesspool, they were worried about rats or rodents coming straight up the pipe into the building. With the water seal right here, the rodent wouldn't go readily through the water. These have fallen out of favor for a lot of reasons. One is you can't just run a drain snake to clear a stoppage. Without the trap, you could come right through, clean the line, and go out and get the tree roots and things like that. Yeah. With a rat trap like this or house trap, I could have a stoppage here, or a partial stoppage, but I could never get at it. Okay, I see. To get around it, they always had clean-outs, and that would let you come in this way or come in that way, but it required that this whole house trap was readily accessible. I would have assumed it was right here at the access point. Now, we know that we're 20 or 22 feet from point A over there, but we don't know whether it's here or over here. It could be outside the building. So, what I've brought is the next generation of this drain camera locator. The camera sends out a transmission signal, and this is a locator to tell exactly where the head of the camera is. It's pretty cool. Let me power it up and we'll find this thing. The head of the camera is sending out a magnetic signal, much like the Earth has a north and a south pole. Yes. The head of the camera represents the equator. So, I'm going to find the two poles. Grab those two red markers. Put one down right underneath me. Okay. Now it tells me the pipe goes this way, and the other pole is right there. Mark it. And guess where the equator is, Rich? Right in the center, we hope. Okay. Right there. Drop your yellow right there. That tells us the exact location of the head of the camera. It also tells us it's 2 feet 8 inches down. That is not pretty, though, because we're going to have to dig all this up if we're going to go after this house trap. Before I have you do that, there's one more thing bugging me, and that is all the water that was in that pipe early on. I think we have to do one more test to determine whether this is the cause of the problem. Let me show you. Let's review. Here's our house trap, and we have a camera sitting right about here, and we can see the water level right here. This whole trap is filled with water. We really want to prove whether we have a partial or full obstruction in the trap or in the line that goes out to the street. In normal operation, when we flush a toilet, this water level should stay where it is. But if there's a little restriction, the level will probably back up. It'll obscure the lens, and it'll take a while to drain back down. So, flush the toilet and give it a test. Okay. Very interesting. We just proved that this trap does not have a restriction, because the water went through it. But I saw the level go down, which makes me want to check one more thing. Do you remember the water we saw early on? Let's pull this back, 15 feet out. There's water. Just a little bit of water. See how it's in the bottom third? Yeah. But now as we come back, see this? At 10 feet out, the pipe is almost filled with water. Still at nine, eight. Now we're back to three, and I started to see the lens again. So from 15 to 3 feet, it's filled with water. That's 12 feet of water in the pipe. I think I know the issue. I think the pipe has sagged. Imagine this house was built 60 years ago. Plumbers would have come along and done these cast iron joints with poured lead, laid them onto sand underneath that bathroom. Over time, maybe the sand let go, the fittings let go, and the pipe sags like this. That pipe now has a place where it sits with water in it. You've created another trap. You end up with a trap out of the house trap, and another one back here. Now you flush a toilet. The air in the pipe needs a place to go. It starts pushing backwards, and that makes the toilet bounce like you have. It might also make the cracks in the fittings under the ground let sewer gas come out underneath. It might seep up through the concrete, and that's where the smells are coming from, I think. So what's the solution? We know from 3 feet to 15 feet that the pipe is sagged. The only way to fix it is to open up that floor, which means a trench in the bathroom, replacing the pipe, and then remodeling the bathroom. If you're going to go that far, you'll be within 3 feet of this. I'd probably get rid of the house trap, too, because then, with all that brand new, it'll pitch properly, it'll vent properly, and you'll have the ability to clear the drain in the future should you need it. That's a big job. It is. Don't shoot the messenger. I'm sorry. I really appreciate you coming and helping us identify the problem, and now we'll work on fixing it. All right, my friend. Thanks for your help. Thank you. You're not always the bearer of bad news. You had some good news back in '02. Yeah, it was a long time ago. These plumbing stories are hard to see when we're out in the field, so I made a little mockup to help understand what's going on inside. This is made out of PVC. It's not exactly to scale, but any house has a main drain and a main vent, a main stack that goes completely out through the roof. We essentially saw that with the clean-out in the basement going up, and it's made of cast iron in this case. This is just PVC. Next to it, there's always a separate stack, called the vent stack. All the systems have to work together. In the case of this building, this represents underneath the toilet on the second floor, and this is the lavatory on the second floor. When you flush the toilet, a big slug of water comes down and pushes down. But there's already air inside this pipe that has to get out of the way somehow. You can't compress this air. Normally it might push that air ahead and out into the sewer, but we have this house trap right here that acts as a resistance point. Air can't go past the water seal inside the trap. We'd love it to go up through this branch, which represents the basement toilet. Here's the basement lavatory. This is called a wet vent, a vent that continues up. But this whole pipe, as we determined in the field, had settled so much that if you look at this fitting, it's more than half filled with water, which means the vent is completely blocked. This is actually smaller than the diameter of the pipe. Correct. Blocked, right? So now we've got a slug of water on this side and a slug of water on that side. The slug of air being compressed has no other choice. It has to push up underneath that basement toilet and bubble through the water seal in the toilet. Every time it bubbles through, you get that sewer gas smell. So this is basically sewer gas that was in the pipes. That's right. Once it bubbled up, you got that smell and the bouncing in the water. The air needed a place to go. You have to have properly vented fixtures in a house for every plumbing fixture to work. Well, this tells that story very well. I hope so. Cool. Great investigation work. Thanks.