Floor Drain Basics
July 28th, 2009 | 15 comments
One of the most common defects that I find in old Minneapolis and Saint Paul houses is missing cleanout plugs in floor drains – especially during Truth In Sale of Housing Evaluations. Missing cleanout plugs can allow hazardous sewer gas in to the home, and often indicate a clogged floor drain. To learn why and how, read on.
Every plumbing fixture has a trap. The purpose of a trap is to prevent foul-smelling sewer gas from coming back in to the house. The diagram at right shows a P-trap, which can be found at sinks, showers, and bath tubs. The left side of the trap connects to the plumbing fixture, and the right side connects to the sewer. The ‘sewer’ side will have sewer gases present, but the water sitting in the bottom of the trap prevents the sewer gases from entering in to the house.
Floor Drain
Floor drains are no exception. The photo at right shows a floor drain, as viewed from the side. The shaded portion shows the trap where water will always sit, which prevents sewer gas from coming in. When you look at an installed floor drain, all that you typically see is the grill on top; the rest of the drain is always buried in the basement floor.
When the drain line gets clogged If the drain line for the floor drain gets clogged, it needs to be cleaned out with a drain cleaning tool. The floor drain has an area which bypasses the trap, which will allow a tool to be inserted in to the drain. I’ve highlighted this bypass in the photo below, left. Normally, a plug is always in place here, because this is an area where sewer gases dwell. When the plug is removed, sewer gases come in to the house. After the drain gets cleaned out, the cleanout plug needs to be replaced. The plug is circled in blue in the photo below, right.
What if the threads are destroyed? On some older floor drains, the threads that used to accept the cleanout plug are damaged or badly rusted, to the point that it’s impossible to screw in the cleanout plug. The only acceptable repair for this situation is to install a rubber plug. One type of plug is a piece of rubber that is sandwiched between two pieces of metal that expand the rubber when tightened together. The two photos below show a rubber plug before it’s tightened and after it’s tightened. Another type of rubber plug can be found here http://www.real-titeplugs.com/real-tite-plugs-uses.html .
A missing cleanout plug usually means one of two things:
- The drain was clogged, someone removed the cleanout plug to clean the drain, and they forgot to put the plug back in.
- The bottom of the trap is clogged, and someone removed the cleanout plug to allow water to drain directly in to the sewer, instead of going through the trap.
Any time I see a missing cleanout plug, I tell my client that the cleanout plug needs to be replaced, and the floor drain may need to be cleaned out or replaced. If the drain cannot be cleaned, the entire floor drain needs to be replaced. When I perform re-inspections on homes in Minneapolis that have had missing cleanout plugs, about one in five floor drains need to be replaced because the drain couldn’t be cleaned out. This is an expensive repair, as it involves breaking up the concrete in the basement floor, replacing the drain, then pouring new concrete.
Just for fun, here are a few photos of missing cleanout plugs that I’ve taken within the past couple months.
For more information on common Truth In Sale of Housing defects, click on any of the links below.
- Missing Jumper Wire
- CO Alarms
- Vacuum Breakers (backflow preventers)
- Toilet Ballcocks
- Smoke Detectors
Reuben Saltzman, Structure Tech Home Inspections – Email - Minnesota Home Inspections
home inspection sussex county
July 31, 2009, 11:12 am
very informational!
Rick Absi
August 17, 2009, 6:46 am
Great article. I’ve been struggling with a sewer odor in our house for a long time, and I think I’ve identified the floor drain as the source. The floor drain is used for condensate from the evaporator coil on the air conditioner. It’s located in the garage. The house is 11 years old, built slab-on-grade. We’re connected to city water/sewer.
I’ve tried to look for the cleanout plug in the drain, but I can’t find it. Is it possible that I have a floor drain without a cleanout? Or am I just missing something? I greatly appreciate your input. The smell is really bad and very annoying! Thank you.
Reuben Saltzman
August 17, 2009, 5:03 pm
Rick – some floor drains don’t have cleanout plugs. Maybe the trap has dried out? If the water dries out, you’ll get sewer gas. Send me a photo or two, and I’ll give you an opinion and post the photos.
Chris Anstey
January 4, 2010, 10:17 pm
I have just recently removed the drain cover from the floor drain in the basement, the drain is blocked but water does seap out very slowly . I noticed this plug on the side of the drain and now understand what it is for . is there any special technique for removing the plug from the drain wall. Drain is cast approximately 60 years of age . Would draino in hoy water help with clearing the floor drain. Any assistace would be appreciated.
Reuben Saltzman
January 5, 2010, 6:25 am
Most old plugs are threaded in place, and can be removed with a pipe wrench. I don’t think any type of liquid drain cleaner would help – I’ve never had any luck with liquid drain cleaners. They’re supposed to work on hair, and I’ve found them to do a marginal job of that. I’d use a ‘snake’, which is slang term for a mechanical drain cleaning tool.
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January 29, 2010, 6:43 am
[...] Floor Drains [...]
Mark Schreiber
March 4, 2010, 2:17 pm
As a response to Rick’s problem and anyone else that is experiencing sewer gases and odors from their floor drains; this is generally because the water traps in the pipes have dried out. This allows the gases to enter into your home or even into your place of work. Over time, the water trap will evaporate if not regularly used or flushed. I have found and researched into a product called TheSureSeal which you can easily place within your floor drain, whether in your bathroom, shower, or even in the water heater drain. TheSureSeal is a device that you can place in your drain in just a matter of minutes. It is very effective and easy to use.
Reuben Saltzman
March 4, 2010, 5:55 pm
Mark – I debated posting your comment because it sounds like you’re trying to sell your goods on my blog. Come now, you didn’t really find and research this product; you’re selling it, right?
I posted your comment anyways because I’ve never seen this product before. What advantages would this product have over pouring some anti-freeze in to the drain, probably at a fraction of the cost?
Mark Schreiber
March 11, 2010, 3:25 pm
Okay well first of all “research the product”. It’s something everyone does. If you go into something blind and don’t research it then you’re sometimes in for a rude awakening.
And to answer your question, it’s not that it kills bacteria which is I suppose what anti-freeze would do, but anti-freeze doesn’t solve the problem of failed water traps. This device prevents the odors that the sewer would otherwise bring up with a failed trap scenario.
Secondly, putting solutions into your pipes can only be worse for the environment. This is chemical free.
Reuben Saltzman
March 11, 2010, 4:05 pm
Very good, thanks.
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March 19, 2010, 11:40 am
[...] Floor Drains [...]
David
April 18, 2010, 5:35 am
I wonder if you can tell me how would I know for sure that a drain in my basement goes to the sewer or if it just goes to a dry bed? I started making a shower around it and had to stop until I figure that one out. I opened the drain cover and there was a 4 inch tube that looked like a pencil that was coming out of the side that felt like it was soft copper as I could bend it. The house is 30 years old in Canada the drain goes down about a foot and turns. There was also a rough in for a toilet and sinc….any help would be appreciated as this project has been on stall for the past year now.
Reuben Saltzman
April 21, 2010, 5:09 am
Hi David,
If you have a main sewer cleanout hole right before your main drain leaves the house, try removing the cover, then pour a bunch of water down the floor drain. If it goes out to the sewer, you’ll be able to see the water from the cleanout hole.
The soft copper tube that you’re referring to is probably a trap primer – it’s a device that will periodically dump a little bit of water in to the floor drain to prevent it from drying out.
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April 26, 2010, 7:44 pm
[...] Floor Drains [...]
David
August 25, 2010, 6:31 am
You are a brilliant man as I have been trying to figure this out for a couple of years and nobody had a clue how to figure out my problem but you did…..THANK YOU….MY DRAIN GOES TO THE SEWER.!!!!