House Trap with Cesspool or Septic tank

[WD8CDH]

Hi,

I know that House Traps are now illegal with most municipal sewer systems, but are they needed with Cesspools or Septic systems?

Thanks,

Ron

[LazyPup]

It is my understanding that their are some areas in New York that still require house traps, but as a rule house traps are outlawed for all applications.

[WD8CDH]

Hi LazyPup,

Thanks for the reply. I just replaced a bunch of rotted cast iron in the basement and noticed that there wasn't a House Trap but there is a house vent exiting the wall about 2 feet above the main sewer line going to the cesspool. Everybody (neighbors, non-plumbers) that I talked to said there has to be a trap between the house and the cesspool (yes, I live in NY).

Should I add a house trap and to which side of the horizontal house vent does it go. The rest of the system does have a roof vent. I am more looking for a technical answer rather than a legal one.

Thanks,

Ron

[LazyPup]

Hi again Ron,,

In order to get a definte answer to you question you would need to call your local plumbing inspection department and find out what your local code says, but in the mean time let us examine the reasoning behind the prohibition of house traps under the National Model codes.

Years ago there were no regulations concerning the proper discharge of sanitary waste and consequently most rural homes just had outhouses. In the cities they had municipal sewers which discharged directly into a local river or estuary. In those days the municipal sewers handle both sanitary waste and storm runoff, therefore the curbside storm grates served a dual purpose as vents for the sewer system.

In those days all houses were required to have a "main house trap" which prevented any sewer gasses present in the municipal sewers from entering the structure.

As we began building sewage treatment plants it was soon realized that a residential structure with a family of 5 will produce an average of 300gal of sanitary waste per day.

On the other hand, an acre of land occupies 43,681sq.ft. Multiplying that by 144sq.in per sq. ft we get 6,290,064sq.in per acre. This means that for each 1/10 of an inch of rainfall we have 27,229gallons of storm runoff per acre, or to put this in perspective, each acre of land served by the storm drains would produce as much water per 1/10" of rainfall as 90 homes would typically produce in 24 hours. As you can see, it was quickly realized that the storm runoff was overwhelming the treatment plants.

In order to resolve that problem the cities then had to put in a second set of sewer lines. The original sewer lines still running to the treatment plants to process sanitary waste. Since the storm runoff was basically plain water it could still be discharged directly into the watershed without concerns about polution.

The problem here was that once the curbside storm grates were rerouted to the storm sewers we no longer had any vents on the municipal sanitary sewers with the minor exception of the little holes in the manhole covers. As a consequence the levels of methane and sulpur dioxide in the sanitary sewers often reached explosive levels. In fact, in 1955 in central Indiana there was a town where the main sanitary sewer under the main street actually blew up, killing dozens of people, and ripping the main street wide open.

It was then determined that we should do away with the house main trap. Once the house trap was removed, as each house was added onto the municipal sewer the house sewer, main drain and main vent were now open from the municipal sewer up through the roof to atmosphere. In this manner every structure attached to the municipal sewer also added additional venting.

The same holds true for septic systems. By keeping the house sewer open from the septic tank to the structure, through the main drain and on up to the main vent it allows any gasses produced in the septic tank to safely vent to the atmosphere.

In those instances were local codes may still require a house trap, it would mean that you would also need a vent on the septic tank side of the house trap to prevent a dangerous buildup of sewer gasses in the septic tank and house sewer line.

One little tidbit of trivia that i found interesting while reading some old plumbing codes had to do with the construction of outhouses. Everyone is familiar with the little half moon cutout commonly seen over the door of an outhouse, but who would have ever guessed that the cutout over the door was code required as a vent?

On a side note, i am curious about the origin of your screen name WD8CDH? Is that by chance an amateur radio call sign? The reason I ask is because I am a ham operator..call sign KC8UXZ General class and licensed continually since 1974.

[WD8CDH]

Hi LazyPup,

Thanks for the explanation. I guess that if there was a House Trap then there MUST be a vent between the House Trap and the Cesspool too. That is the way most of the houses here on Long Island are plumbed. Also that vent is down low, usually only a foot above grade where it comes out of the foundation.

Without a House Trap, should there still be (technically) that low house vent or just the roof vents? My house has no House Trap but it does have the low vent (in an enclosed patio of course???)

Another question, you showed that a sanitary T should not have the side port pointing up and the run horizontal (which is of course the way everything is here on LI) and a Wye and 1/8 bend or combo should be used that way instead. How about if a branch goes into a horizontal main ftom the side? Can a sanitary T be used that way or must it be a Wye and 1/8 bend or combo there too? Or how about if the branch comes in the side at 45 degrees from horizontal? Can that be a sanitary T? Sometimes there is very little room between the floor joists and the main to come in vertically.

I also am a Ham, Extra class. Licensed since the very early '70s too.

Ron

[LazyPup]

The codes prohibit the use of Sanitary Tee's on a horizontal line for two reasons.
With a Sanitary Tee, as the liquid discharging from a horizontal or vertical branch line into a horizontal line through a tee, the liquid will go to the opposite wall of the horizontal line, hit the wall then be forced to change direction. This will 1. Cause a serious restriction in the velocity of flow and 2. it permits a small amount of the effluent to temporarily backflow upstream in the horizontal line where it will eventually come to a halt, then begin flowing downstream.

The resultant loss of velocity will cause any solid waste present in the liquid to settle to the bottom of the pipe where it remains after the liquid flows away. Those solids then dry in place and form clogs.

The solution is to use a Wye & 1/8 bend or combo that bends 45 deg before entering the horizontal line, thus directing the flow in the downstream direction and maintaining the proper velocity of flow to insure any solids will be carried away.

We may not use a Wye & 1/8 bend or combo to connect a horizontal line to a vertical stack because the opening of the Wye is below the bottom level of the horizontal line and as the liquid drops in the 45deg section of the Wye it restricts the movement of vent air.

[WD8CDH]

Hi LazyPup,

Can a Wye be used to connect a 45 degree line to a vertical stack? Or are 45 degree lines a no-no?

Thanks,

Ron

[LazyPup]

The minimum angle for a vent below the flood level rim of the highest fixture served is 45 deg. therefore a 45 deg line may connect to a vertical stack via a wye.

[WD8CDH]

Could that be either a 45 deg vent or drain line or just 45 deg vent?

Thanks,

Ron

[LazyPup]

In can be a vent or branch drain, either one.