Weir-d Science, how a P-trap works

This picture post will attempt to show how a P-trap functions, or more importantly what makes them function.

Notice how the weir can see the vent opening?

P-traps have for the most part replaced most other kinds of traps—notably the S-trap.  The toilet is one notable exception—it is designed to be siphoning—the more siphoning the better.  You want to hear that glug glug glug.

S-trap

Many inspectors are under the false impression that merely lengthening the trap arm will eliminate the S-trap, but what this actually does is increase the potential for siphoning of the trap as the slug of water attempts to go down the drain.  It is a similar principle to how a toilet siphons.

Still an S-trap

The configuration still makes an “S,” just an odd shaped S is all.

What makes the P-trap function is the vent, and the rules that guide where that vent has to be. 

Essentially the vent has to be at least two pipe diameters away from the Weir.  The Weir is where water either starts to go down the drain after the trap or stops going down the drain.  So in a typical 1-1/2″ kitchen sink drain that would be a minimum of 3″ away.

The P-trap rules

We also have to be careful to not get the vent too far away from the weir as the trap arm could flood and block the vent–essentially returning the assembly to more of an S-trap. 

The rules of how far away it can be has to do with the diameter of the pipe (trap arm).  The bigger the diameter the longer the weir can “see” the vent.

Charles Buell, real estate inspections in Seattle

What’s a little raw sewage between friends?

OK–nasty subject–I get that, but what is an inspector to do?

These sorts of issues are considered life/safety issues and the purpose of modern plumbing is to keep “stuff” where it belongs.  We like it when the drinking water stays in the pipes, the waste stuff stays in the pipes and the two don’t get mixed together.

ejectorpump1This sounds like a good plan.

I don’t like sewage ejector pumps–but they exist so I have to deal with them occasionally.  They are common whenever you have plumbing fixtures that cannot drain by gravity.  The effluent has to be pumped up to a level where it can drain by gravity.

Homeowner installation of these devices is almost always obvious and tragic.  At a recent inspection I found one in the basement of a home where a non-conforming kitchen and bathroom had been added.  The bathroom properly drained to the sump below the surface of the basement floor.

The kitchen sink drain however was tied into what amounted to the vent pipe for the unit (the lower pipe that runs off to the right).  However, because there was a big hole cut in the sump cover, no vent was really necessary for the pump to function.  The vent is there because under normal operation a vacuum would be created if it was not there.  A vacuum could suck the water out of the traps of the fixtures it was servicing.  The hole in the cover eliminates any possibility of there ever being a vacuum created.

There also has to be a check valve to prevent water that has been pumped out from draining back into the sump.  There also has to be a gate valve and unions so that the unit can be taken apart to be serviced.  Most importantly there HAS TO BE A SEALED LID!

ejectorpump2

Without a sealed lid the sewage could flood the basement if the pump were to fail–not to mention the likely continual odors of sewage that would be present.

I can only guess why anyone would destroy a perfectly good lid to create this health and safety issue.

The installation needs a new lid—but more importantly it needs a licensed plumber.

By Charles Buell, Real Estate Inspections in Seattle

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What is the future of garbage disposers?

While some jurisdictions are actually wrestling with the notion of banning garbage disposers altogether, and some jurisdictions already ban them for use if a septic system is involved, this post is not really about that kind of future.

This post is perhaps closer to “Back to the Future” in terms of credulity.

In general, I attempt to keep my cool during an inspection but sometimes it is just not possible and when I saw this particular “future” I could not help but laugh out loud.

It is not unusual to see buckets placed strategically under sinks.  The rings and stains inside this pan were certainly consistent with past, present and future leaks.

When I tried to remove the “future” from the pan to see if there was any water in the pan, I discovered that the future was actually holding the disposer in place–and without it, the whole thing would just collapse into the pan.

While it is not uncommon to see disposers at the end of their expected life, I am reasonably certain this one was WAY beyond its expected life and that its future will involve a dumpster.

By Charles Buell, Real Estate Inspections in Seattle

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