P-traps—installing them properly

I don’t go out of my way to be a nit picker as a Seattle Home Inspector—-sometimes it just happens.  I think the kind of nit picker that most agents have a problem with is when those seemingly unimportant items end up in the “Summary of Significant Findings” section of the report.  This is “bad form”—-as Captain Hook would say.  While this kind of information should be mentioned in the context of general “information” about the home, placing it in the Summary gives it “weight” that it doesn’t deserve.

Take for example this P-trap connection at a Garbage disposal.

Improper P-trap

Improper P-trap

At first glance it looks almost normal, when actually it is installed backwards.

With the next couple of pictures, I will attempt to explain what is wrong with this installation.

Traps are engineered to be self scouring (cleaning) by virtue of their shape.  Note how in the first picture below the flow of water enters from the sink (disposal in this case) at Point C and the blue arrow.  The force of the flow of water accelerates when it hits the bottom helping it flow up and over the hill and down the drain at the left blue arrow.

In the bottom picture we can see that when the trap is installed “backwards” the distance labeled “B” is much greater than distance “A”—–a much higher hill for the water to get over.  It also doesn’t have the help of acceleration provided by its being installed the other way.  The flow of water is actually reduced because the flow of water runs into a more vertical wall in the lower installation.

Improper P-trap

What the P-trap should not look like and then what it should look like.

So what will happen if this is not fixed?  Well eventually the trap will clog up with debris and water will just not drain properly.  It isn’t “typically” a difficult fix (although there are instances where it might be fairly difficult)—something any plumber can do when they are at the home for other reasons or something that even a knowledgeable homeowner or other qualified repair person can fix.

It just isn’t the sort of “deal killer” or “safety” issue that warrants placing it on the summary.

***

Charles Buell, Seattle Home Inspector

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Comments

  1. Also the tail ends always go inside the receiving piece in the direction of the flow.
    I put all defects, big or small, in the summary because agents don’t look at or print out the main report. I put significant concerns at the beginning of report

    • Charles Buell says:

      Daniel, with my reports I just don’t do that. It would just make the summary cumbersome for no reason. Only safety issues and defects of “significance” make the summary—along with a carefully worded warning to read the whole report because there “will” be things in the body of the report that the client would also like addressed. I stress that the summary is my opinion and should be added to as they deem necessary.

  2. Great explanation, great photos. I’m going to start linking to this blog post in my inspection reports.

    • Charles Buell says:

      Thanks Reuben. I was just thinking about you. Took a picture on my morning walk of a house with zinc strips—the picture is coming your way soon :)

  3. Isaac Toko says:

    Hey Charles,

    Great info. I was wondering if you had any knowledge, since you are a local inspector, of any areas around the Puget Sound that would be susceptible to cases where there were no p-traps installed at all? I’d expect you’d come across a ton of homes that are older that have some interesting plumbling practices. I work with PSE as a emergency responder for natural gas emergencies and am trying to get information for our area where if there was a natural gas odor in the sewer/storm drains if certain houses of certain ages would be more susceptible to infiltration into the house. I’d really appreciate your help.

    • Charles Buell says:

      Isaac, all homes are going to have some means of trapping against sewer gases. Some homes have no trap on the main drain itself from the home. When this is the case any trap that is not used for a long time can dry out and sewer gases from the city sewer can then enter the home when the house is under negative pressure. Quite common really.

  4. Guadalupe Sabillon says:

    I have a question about if a p trap can be placed at 1 m of the sink? It would work the same way? Or is neccesary to be right below the sink?

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