Is it one clogged drain or my main sewer line?

How is my home's drain system laid out?

Every fixture in your house has a trap (the U-shaped bend that holds water and blocks sewer gas) and a branch drain. Branch drains from a bathroom group join a vertical stack. Stacks and the kitchen line all drop to the main drain, also called the building drain, which runs under the basement floor or slab. From there the pipe leaves the foundation as the sewer lateral and runs to the sewer main in the street or, outside sewered areas, to a septic tank.

Water only flows one way through this tree, so a blockage affects everything downstream of it. A clog in a bathroom sink's trap arm bothers only that sink. A clog in the main drain backs up every fixture above it, starting with the lowest one because that is where the water rises first. That simple fact is the whole diagnostic.

How can I tell which one I have?

Walk through the house and note which drains are slow, which are backing up, and which are fine. Then compare against these patterns:

• One fixture slow, everything else normal: a branch clog. Hair, soap, food, or an object in that fixture's trap or trap arm.
• Two fixtures in the same bathroom slow: a clog in the shared branch or the stack below that bathroom, still upstream of the main.
• Toilets, tubs, and the basement floor drain all affected, especially on the lowest level: the main drain or sewer lateral.
• Gurgling from a toilet or tub when a washer drains or a sink empties: air being forced back through a trap because the main line is partly blocked.
• Sewage or gray water at the floor drain or coming up through a first-floor shower: main line, and stop using water.
• A house with no basement makes this harder to spot, because the first sign may be a first-floor toilet that flushes slowly or a shower drain that fills while the washer runs.

What is the toilet-and-tub test?

The quickest check takes one minute. Go to the lowest bathroom in the house. Flush the toilet and watch the tub or shower drain. If water bubbles up or rises in the tub, the toilet's water had nowhere to go downstream and pushed back through the nearest low opening. That is a main-line blockage below that bathroom, not a toilet clog.

The reverse also tells you something. If the toilet flushes normally but the tub is slow on its own, the tub's branch is the problem. If a plunger on the toilet moves water in the tub, same answer: they share a blocked line. Do the same test at the basement floor drain if you have one. Running the kitchen sink or a load of laundry and watching the floor drain shows whether the main is taking water at all.

What usually causes each kind of clog?

Branch clogs are almost always what went down the drain: hair and soap in bathrooms, grease and food in kitchens, lint in laundry lines, wipes and hygiene products in toilets. They are annoying but contained.

Main-line and lateral blockages have bigger causes. Tree roots find the joints in clay laterals and grow into a mat. Grease from years of kitchen use builds up along the bottom of a cast-iron main. A belly, where the pipe has sagged, holds water and solids that never fully flush. An offset joint or a collapsed section stops the cable cold. In Philadelphia, a full house trap or a broken curb trap does the same. And in heavy rain, a combined sewer can surcharge and push water back up the lateral even when your pipe is clean. Each of these looks like the same backup from inside the house, which is why the fix starts with looking inside the pipe.

What should I do right now?

If the pattern points to the main line, stop running water everywhere in the house. Every flush, shower, and dishwasher cycle adds water that will come out at the lowest drain. Keep people out of any standing water; a sewer backup is not clean. Then reach us.

We clear the main from a cleanout or the house trap with a cable sized for the line, and we camera the pipe to see what caused the block. You get the picture and the options: cleaning alone, jetting for grease or roots, a spot repair, or replacement if the pipe has failed. Options come before work, with permits and inspections handled where Philadelphia L&I or your township requires them. If it turns out to be a branch clog, that is a quicker visit, and we will still show you what came out.