Customer Says Drains Are Slow Everywhere: Translation Decision Tree

Why this matters

"All my drains are slow" is the one drain complaint you cannot treat as a single clogged fixture. When every drain in the house slows together, the fault is almost never at any one trap; it is downstream where all the branches meet, in the main line, in the building drain, or in the venting that lets them flow. Treat it like a local clog and you will snake a sink that drains into a backing-up main and call it fixed an hour before it overflows again. This tree translates "slow everywhere" into the real location: a common downstream restriction, a vent problem, or a sewer-side failure.

Symptom presentation

The pattern tells the story. "Everything slow, lowest fixtures back up first" is a main-line or building-drain restriction; gravity loads the lowest drains first. "Slow plus gurgling and bubbling at other fixtures" is venting or a partial main blockage pulling air through traps. "Slow only on one floor or one branch" is not truly whole-house; it is that branch's line. "Slow and getting worse over weeks" is a building restriction growing (grease, roots, scale, a belly collecting solids). "Slow right after heavy rain" points to groundwater infiltration or a compromised sewer. "Toilet bubbles when the washer drains" is a classic shared-main symptom. Pin the variant before pulling a single trap.

Quick checks

• Run water at the lowest fixture (basement floor drain, lowest tub) and watch for backup; the lowest fixture is your early-warning gauge for a main problem.
• Flush a toilet and listen at nearby fixtures for gurgling, which signals a vent or partial-main air problem.
• Check whether it is genuinely every fixture or just the ones on one branch; test fixtures on different stacks.
• Look for and open the main cleanout. If water stands in the cleanout, the blockage is downstream of it (main/sewer); if the cleanout is dry but fixtures are slow, the restriction is between the fixtures and the cleanout.
• Note any recent change: new fixture, recent rooter work, recent landscaping over the sewer path.

Isolation tree

Branch A, lowest fixtures back up, cleanout holds water. The restriction is in the main or building sewer downstream of the cleanout. Causes: root intrusion at a joint, grease and solids accumulation, a pipe belly (sag) collecting debris, scale in old cast iron, or a partial collapse. Confirm with a camera run from the cleanout to find the type and location.

Branch B, slow everywhere with widespread gurgling, no standing water at cleanout. Suspect a vent problem: a blocked or frozen vent stack, a bird nest or debris in the vent, or insufficient venting. Without venting, draining fixtures pull a vacuum that slows flow and siphons traps (you may also smell sewer gas). Check the roof vent termination and test by flushing while listening at multiple traps.

Branch C, slow confined to one stack or branch. Re-translate: this is a branch-line clog, not a whole-house problem. The customer perceived it as "everywhere" because several connected fixtures share that branch. Snake or clear that branch line.

Branch D, worsens after rain or seasonally. Groundwater infiltration through cracked sewer joints or a compromised line raises the water level and slows everything. A camera after rain shows water entering. This often pairs with root intrusion at the same cracks.

Branch E, intermittent backup with sewage odor and multiple-fixture involvement. Main-line blockage near full obstruction. Treat as urgent: stop water use, open the cleanout to relieve pressure, and clear or camera the main before any further fixture use.

Confirming diagnosis

Confirm at the cleanout and the camera, not at a single trap. Standing water in the main cleanout proves a downstream main/sewer restriction and tells you where to clear from. A camera run identifies type (roots, grease, belly, scale, collapse) and distance, which determines the right tool (cable rooter, hydro-jet, or excavation/lining). Gurgling across fixtures during a flush confirms a vent or near-full main. The diagnosis is not done until you know whether you are clearing a vent, cabling roots, jetting grease, or scoping a collapse.

Remediation

Match the tool to the finding: clear the vent (remove debris from the stack), cable or hydro-jet the main for roots, grease, and scale, or recommend repair/replacement (point repair, trenchless lining, or excavation) for a belly, collapse, or repeated root intrusion. For infiltration, locate and seal or line the cracked section. After clearing, re-camera to confirm a clean line, run water at the lowest fixture to verify free flow, and document the cause so a recurring main gets a permanent fix, not another snake.

References

• 2021 Uniform Plumbing Code (UPC), Chapter 7, Sanitary Drainage, and Chapter 9, Vents.
• 2021 International Plumbing Code (IPC), Chapter 7, Sanitary Drainage, and Chapter 9, Vents and Venting.
• 2021 International Residential Code (IRC), Part VII, Plumbing, drainage and vent provisions.
• ASSE / IAPMO field practice for sewer cleanout access and camera inspection.