A basement floor drain has one job, to take water off the floor, and when it does the opposite the whole basement knows about it. Because it is the lowest opening in the drain system, it is the first place a main line problem shows: when the lateral blocks, the toilet upstairs still flushes, the water goes down the stack and comes back up the floor drain. But a floor drain also has its own trap, its own short branch and its own ways of blocking, and the difference between a drain problem and a main problem is the difference between a small-head scope through the grate and a full reel from the cleanout.
Quick answer: if the floor drain backs up only when other fixtures run, the problem is downstream in the building drain or the lateral, and the camera goes in from the main cleanout. If it backs up on its own, or the trap is full of sediment and holds water, the problem is the drain’s trap or branch, and a small camera goes in through the grate. If it backs up in heavy rain with clear water, the public main is surcharged or a storm connection is overwhelming the lateral. The timing is the diagnosis; the camera confirms it.
Reading the timing
Backs up when the washer drains or the toilet flushes: main line. Backs up when it rains: surcharged main or storm connection. Holds water all the time and smells: sediment in the trap or a dry trap refilled with scum. Backs up when the water heater drains into it or the furnace condensate runs: its own branch. Each pattern points at a different pipe, and the whole-house slowdown guide covers the main line case in detail.
The drain itself
Under the grate is a trap, usually a deep seal trap in a cast iron or plastic body, with a branch leaving it to the building drain. Sediment, laundry lint, hair and concrete dust from the floor collect in the trap until it holds water and drains slowly. In older houses the branch is galvanized or cast iron and narrows with rust. A small camera through the grate shows the trap bed, the branch and its connection. The fix for sediment is to clean the trap; the fix for a rusted branch is to replace it. Camera inspection of a basement floor drain covers the procedure, and entering from a floor drain the technique.
The main line
If the timing says main line, the inspection starts at the main cleanout, not the floor drain, with a full reel. The camera looks for the usual causes: a root mass, a grease plug, a belly, a scaled cast iron section, a collapsed section, or in an old house a channeled building drain under the slab. The floor drain was only the messenger. The basement drain camera guide covers the equipment, and the under-slab cast iron guide the most expensive finding.
The rain case
Clear water rising in the floor drain during or after heavy rain, with the house’s own drains working, means water is coming from outside. Either the public main is surcharged and backing up every lateral on the street, or a downspout, a sump or a foundation drain is tied into the lateral and overwhelming it. A camera in the lateral during rain shows the flow direction and any side entry carrying clear water. The fix is a backwater valve for the first case and disconnection for the second. The stormwater connection guide and the backwater valve guide cover both.
What to record
Which fixtures were running when it backed up, and the weather. Whether the trap holds water between events. What the small camera found in the trap and branch. What the full reel found in the main, with distances. And whether the house has a backwater valve, where it is and whether it was checked. A floor drain backup that is written up as “cleared floor drain” when the cause was the lateral will be back.
Entering through the grate
Lift the grate, which is usually held by two screws or simply sits in a recess, and look into the trap. Sediment, lint and scum are often visible and can be scooped out before any camera goes in. Feed a 17 or 18 mm head on a 5 mm rod through the trap with water in it; the head makes the bend if fed gently and rotated. The branch beyond is short in most houses and joins the building drain within a few feet, so 30 ft of cable is usually plenty. If the small head stops at a rust lip in a galvanized branch, that is the finding, and the branch is replaced rather than cleaned.
What to record
Which fixtures were running when the backup happened, the weather, whether the trap held water, what was removed from it, the condition and material of the branch, and, if the main was inspected, the findings with distances. A backup written up as “floor drain cleared” when the cause was the lateral will be back with the next flush.
Common questions
Why does water come up my floor drain when I flush?
The main line is partly blocked and the floor drain is the lowest opening. Inspect from the main cleanout.
Can I camera a floor drain?
With a 17 or 18 mm head through the grate, yes, for the trap and branch. The main needs a full reel from a cleanout.
Why does the floor drain back up in rain?
Either the public main is surcharged or stormwater is tied into your lateral. A backwater valve or a disconnection is the fix.
Related guides
See basement homes: floor drain and main line inspection, inspection after a basement flood, and multiple fixtures backing up.