A slow bathroom sink is a hair clog in a trap arm. A slow kitchen sink is grease in a branch. But when the toilet flushes sluggishly, the tub takes an hour to empty and the basement floor drain holds water, the problem is downstream of all of them, in the building drain or the lateral, and the sink-by-sink approach will never find it. A whole-house slowdown is the classic reason for a sewer camera inspection from the main cleanout, and the pattern of symptoms narrows the possibilities before the camera goes in.
Quick answer: all drains slow at once means a partial obstruction, a belly or a capacity problem in the main line, or occasionally a blocked vent that starves the system of air. The camera from the main cleanout shows which: a root mass or grease plug partly closing the bore, a belly holding water and sediment, a collapsed or deformed section, or a clear line with no obstruction, which points at the vent or at a surcharged main. The lowest fixture in the house backs up first, which is why the floor drain is the early warning.
Reading the symptom pattern
Slow everywhere but no backup: a partial obstruction or a belly that still passes flow. Lowest fixture backing up when others run: a main line obstruction, with the floor drain or the basement shower taking the overflow. Gurgling at one fixture when another drains: air being pulled through traps, which means the main is partly blocked or the vent is restricted. Slow in wet weather only: a surcharged main or infiltration filling the lateral. Each pattern is worth noting before the inspection because it tells the operator where to look first. The gurgling guide covers the air side.
What the camera finds, in order of likelihood
A root mass or grease plug that has closed most of the bore but not all of it, so flow passes slowly. The camera reaches it, the picture shows the partial opening, and the distance reading places it. A belly holding water and a bed of sediment, which slows everything upstream without blocking it. A scaled cast iron section whose bore has narrowed. A deformed or partly collapsed section. And, in a line that looks clear from end to end, nothing, which sends the diagnosis to the vent or the main. Reading standing water separates the belly from the obstruction.
Where to enter
The main cleanout nearest the foundation, pushing toward the street, covers the lateral. A two-way cleanout or the test tee at the stack base covers the building drain back toward the fixtures. If the house has neither, the roof vent gives access to the stack and the building drain below it. A whole-house problem is usually in the lateral or the building drain, and the inspection should cover both if the first pass finds nothing. The cleanout guide explains the entry points.
When the line is clear
A clear lateral and a clear building drain with every drain still slow point at the vent. A blocked or undersized vent means the draining water cannot pull air behind it, so every fixture drains slowly and traps gurgle. The camera can inspect the vent from the roof, looking for a nest, leaves, a collapsed section or a frost cap of ice in winter. Vent stack problems covers it. The other possibility is the public main itself, surcharged in wet weather, which the utility must address.
What not to do
Do not pour chemical cleaner into every fixture; it does nothing for a main line problem and it sits in the pipe waiting for the camera head. Do not cable each fixture separately; the problem is downstream of all of them. Do not accept “the line needs jetting” without seeing the footage that shows what is in it, because a belly or a collapse does not respond to jetting. And do not ignore a floor drain that holds water; it is the lowest point and the first warning of a main line obstruction. Inspection upsells to watch for covers the jetting case.
After the diagnosis
An obstruction is cleared, then the camera checks the pipe at that spot for the defect that caught it. A belly is a repair decision based on depth and history. A scaled section is a descaling and lining or replacement decision. A vent fault is cleared from the roof. In every case the second camera pass confirms the fix and gives the house a baseline recording for the next time a drain slows. Re-inspecting after a repair explains why the second pass matters.
What to record
Which fixtures are slow and which back up, the weather, and whether the floor drain holds water. Then the camera’s findings with distances: the obstruction or belly, or the fact that the lateral and building drain are clear. A report that says only “line jetted” after a whole-house slowdown has not diagnosed anything, and the next slowdown will need the same work again.
Common questions
Why are all my drains slow at once?
The fault is downstream of all of them: the building drain, the lateral or the vent. A camera from the main cleanout finds it.
Can a vent problem make drains slow?
Yes. Without air behind the water, every fixture drains slowly and gurgles. Check the vent if the main line is clear.
Which fixture backs up first?
The lowest: a basement floor drain, a basement shower or a first-floor tub. It is the early warning of a main line problem.
Related guides
See multiple fixtures backing up, the best sewer cameras for residential inspection, and can a sewer camera find a blockage.