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Question DetailsAsked on 5/2/2016

Sewer Problems: What's happening?

A couple months back, our sewer line backed up and overflow entered our basement laundry room. We had a plumber come to help. Kind of a side note: There doesn't seem to be a clean out on our house. It was built in the 1930's, and we cannot locate one. Anyway, plumber sent ~100ft of snake through the line, all the way to the alley and scoped it with a camera as well. Nothing. We had the city come by after and they jetted their line (which runs in the alley). This resolved the problem right away. Yesterday, it happened again. We skipped the plumber this time and just started with the city, who with some convincing, came by and jetted the line. This again resolved the problem. The overflow had a kind of a gritty, silty texture to it... not paper. Does anyone have a suggestion as to what's the root of the problem? I want to avoid spending thousands if it's something in the city infrastructure. They (the city) is hesitant to claim fault on anything.

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I am going to assume you have a gravity flow system, not a pressurized sewer system where you have a pump that ejects your sewage to the city system under pressure. If it is a presurized system and you have backflow, then the backflow checkvalves in the sewage pump are not working right.

On the gritty/silty texture - sewer main flow tends to be gritty and sandy - the solids and paper tend to get broken up and start to biodegrade pretty quickly, leaving a fairly homogeneous sludgy flow (with floatables remaining on top of course).


Sounds like your basement laundry room is close to the elevation of the street sewer, and they have an intermittent or chronic blockage situation. Could be you have a line coming in downstream of the sewer you dump into which is carrying a lot of sediment so it is intermittently blocking off the street sewer line you are on, causing a blockage at the outlet. Could also be, if you have combined sewers (storm sewers and street runoff both go into the sanitary sewer) that too much street grit is getting into the sewer and blocking it - either at an outlet of the branch you are on, or possibly even at the outlet of your line to the street line, basically because the street sewer is filling partly with sediment from time to time - would commonly occur after rains if that is the case, though backup would also occur during heavy rains due to any high water event in the sewers - due to backup due to debris or sediment, or due to inadequate flow capacity. Could also be a localized pertial pipe collapse, letting soil in which is blocking the flow at times.

To prove to the city it is their problem you would have to (next time it happens) have the plumber run the camera through without first jetting or routing out the line (if he will agree to do that), to prove it is backing up without any blockage in your line. Also, a statement on the invoice that no blockage was found in your lines and the backup is from the public sewer is necessary as proof that your line is clear and draining properly.

However, it is quite possible, especially if your basement drain is below the street sewer manhole elevation (where sewage would run out If the public sewer backed up), they will tell you that you should put a backflow preventer or sewage lift pump in your house.

Backflow preventers are spring-loaded valves that are supposed to only allow the flow to go one way - out. In preactice they commonly allow a small amount of backflow as the sealing lips leak a bit due to sediment or paper getting caught on them, and they also do not work well with a small differential hydraulic head across them. Generally work well if the line feeding into them is 4-6 feet or more above the valve - poorly if the line the sewage is going into is only a foot or two below the backflow preventer or there is no significant elevation difference between the incoming flow and the preventer.

A more positive way to avoid the problem, but more capital and maintenance cost, is to put all the basement drains on a sewage lift pump, which catches the drainage in a small tank (generally inset into the basement slab) and pumps it up to the main floor piping, which then drains down from maybe (depending on pipe burial depth due to frost depth) from a half dozen feet to as much as 15 feet into the line running to the street, preventing backup unless your main floor is so low that during flooding it gets flooded, in which case the sewers would also commonly back up to the same level regardless.

Third solution if the laundry room is the ONLY water usage point in the basement - though requires you take positive steps before and after using laundry and does not work if you have connected basement floor drains - is to put a manual shutoff valve on the drain line from the washer/washtub which you manually open and close every time you do laundry. I suppose you could put an automatic electrically controlled one there too but would be hard to rig so it does not open if backflow occurs, which is something you can watch for if you open it manually - so do not do laundry if backflowing. Does mean if you forget to open it the washer drainage overflows, and if you forget to close it after the washer is done that you can still get backflow when the water level next builds up in the street sewer.

Fourth option, again if the washer is the only drain in the basement - is to run the discharge hose as high as the washer manual says it will work to discharge into the drain pipe leading to the sewer - which might (would have to be measured) get the discharge point higher than the street manholes so should not backflow under those conditions.

Most of these solutions call for modifying your sewer line so the first floor line drains through solid pipe (with no openings or drains) to the line to the street, and the basement drainage/sewage is lifted up to the first floor level piping for discharge.

When the jetting by the city solved the problem you should have gotten on the record (with you keeping a record of case numbers) that the problem was solved by the jetting. At this point, perhaps the thing is to talk to someone in engineering at the sewer utility about getting a camera (or physical if large enough sewer line) inspection of their system to see if there is a partial blockage, improper slope, excess debris coming in from a storm sewer or maybe a partial cave-in, etc.

If the city will not help, a Civil Engineering firm (not an AL category) which deals in residential drainage and sewage issues would be the professional to contact.

I would also talk to the neighbors to see if they have had this sort of problme - if so, a joint letter to the sewer utilitiy would carry more weight than just your complaint. Your neighbors, if this is due to house sewer pipe being near to the same elevation as the street sewer line, may also have gone through the same process and gotten one of the above mentioned options installed. Their experience might help you decide which way to go, and give you an idea of what they paid.

Answered 2 years ago by LCD

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