vent line on street and on roof?

My mom's house in SE Pennsylvania has a vent system that I am not familiar with and I am hoping for some advice to see if there are some alternatives to try before excavating the pipe in question.
Every house along my Mom's steet has a vent cap between the curb and the sidewalk. The toilets at her place have to be flushed several times and/or plunged in order to get solids through. A sewer cleaning service visited the house and based on what they observed, they started snaking via what they referred to as the "street vent." They could get no further than about 6'. Apparently there is something wedged in the trap that they can't get out. They did get out two bricks and a bunch of stones so they think there is more of the same blocking the trap. The city came out and replaced the vent cap and part of the line, but said the problem extends onto the property. [fyi, a neighbor's kid dumped the stones through the vent cap holes, but I don't understand the bricks]
What is the purpose of a vent line with a trap that runs to the street? Is it possible that the vent pipe that goes to the roof is sufficient and the real problem is a blocked drainage line? When the sewer cleaners talked about a "vent line" is it possible that this is also the same as the drainage line?
Is it worthwhile to pay (~$350) for the sewer cleaning company to return and clean the drain lines and/or roof vent before paying a plumber to dig up the buried vent line and trap (~$1500?). Thanks for any insights.
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"Rald" <
What you're refering to is a "house trap" with it's vent. It's of a bygone era, and they haven't been installed since for about 80 years in most places. The thinking was, I guess, to protect the house from the street sewer. We realize now that it's superflous. The vent that goes through your roof is sufficient protection.
The best thing is to get rid of the trap. There'd be no reason to replace the whole line, just the trap. Shop around, and maybe you'll find a price cheaper than $1500. How deep is it? Maybe you could dig it yourself! When it's replaced, make sure you put in a cleanout in the lawn.
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Me....I believe in the whole house trap. Can we all start a fight now ?

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"Red Jacket"

If you install them, or if your city still installs them, then maybe we can fight. I can't remember if I like you or not. If you're a plumber, then we'd never fight; we'd only discuss.
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Id figure out where the clog was first. Is there a "main cleanout" where sewer leaves house? Snake from there out or from the street vent back. I am suprized the city does not count the trap as their problem if it is right at the point where it enters city main and they did take care of the vent; which I assume is upstream. Check with your local auth. but its true you could prob get rid of it all. Id definitely get rid of the vent if I got rid of the trap. (convert vent into clean-out)

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Ned Flanders wrote:

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Thanks for the input so far. It seems that the house trap accessable via the steet vent cap is redundant with the the roof vent. If it is truly redundant, shouldn't I be able to ignore that the house trap is partially obstructed and just pay to have the drain line snaked through a toilet or the roof vent to solve the slow drain problem?
If the house trap is NOT redundant with the roof vent, then I should put the money of a potentially unneeded snaking towards replacing the obstructed house trap. Does that sound right?
Rald
P.S. It seems strange that some refer to this as a "house vent" if it actually has a trap in the line. Why would anyone vent the sewer smell venting to this steet? I am not a plumber (obviously) and don't have a good picture of what's going on, but I am very curious how this whole house trap business is suppose to work. Any description are greatly appreciated.
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I assumed the vent was upstream of the trap in order to stop the smell from getting out. I can think of no other reason for the trap at all. I guess if it was left accessable then one could argue it gives you a chance to get stuff before it enters city line and clogs that. It must be code if everyone has it. Perhaps whats his face can give us a good reason for this set-up if he is such a fan. Is the point to keep stuff outside of the house if the city main clogs?? Bottom line is find out if it is code to have it, if not then remove both trap and vent. ( this assumes you are within required distance to city main to not require an aditional vent.)

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We call that vent up here a F.A.I. (fresh air inlet). The trap is or was called a building trap, which was to prevent the sewer gases form entering the building via the building drain and up the soil stacks and waste stacks and thus thru your roof or stack vent. We've done away with them here, most old houses that haven't had there building drains replaced still have them. We still use building drains however on storm systems that are used in a combined system, to prevent gases from exiting roof drains or balconies drains. Building traps don't do much in the way of stopping a backed up sewer from entering your house, you would need a back water valve for that job.
Andrew

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I meant the vent. wouldn't iot come out the street vent first?

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