A basement bathroom is the most common major plumbing addition to an existing house, and it is also the one that depends most on a pipe nobody has seen. The new fixtures connect to the building drain under the slab, or to an ejector pit that pumps up to it, and the whole project assumes that drain is deep enough, sound enough and routed where the plans think it is. A camera inspection before the design is finished is how those assumptions get checked.
Quick answer: before a basement bathroom, camera the building drain from the cleanout toward the street and, if possible, from a floor drain or the stack, and use the sonde to mark the drain’s route and depth across the slab. Confirm whether the drain is deep enough below the new fixtures for gravity flow or whether an ejector pit is needed, check for bellies, channeled cast iron and offsets that the new load will aggravate, and record the footage as the baseline. Repair anything found before the slab is closed.
Why the drain’s depth decides the design
A toilet needs its outlet above the drain it joins, with fall between them. If the building drain runs shallow under the slab, a basement toilet can connect to it by gravity; if it runs deep or exits the house above the basement floor, the new fixtures need an ejector pit and pump. The difference is thousands of dollars and a mechanical device that will one day fail. The camera, with the sonde and a receiver, finds the drain’s actual depth at the point where the new bathroom will connect. Locating the head underground describes the method, and typical sewer depths sets expectations.
Mapping the route across the slab
Plans of an old house rarely show where the building drain actually runs. The camera pushed from the cleanout, with the head located every few feet from above, draws the route on the floor in paint. The bathroom is then placed where the connection is short and the saw cut is small, rather than where a guess put it. A drain that turns out to run under the proposed shower wall changes the layout before anything is demolished.
What the camera checks in the existing drain
Cast iron building drains from the 1950s to 1970s are the usual case, and the camera looks for channeling along the bottom, scale that narrows the bore, and cracked or offset joints at the hubs. Clay or Orangeburg, where the drain leaves the house, has its own problems. A drain that is already failing should be replaced where the slab is open anyway, not connected to. Cast iron inspection priorities covers what to look for.
Bellies under the slab
A belly in the building drain is a low spot where the slab has settled or the pipe was laid badly. A new toilet discharging into a bellied drain makes a standing-water trap worse and invites backups into the new bathroom, which is the lowest fixture in the house. The camera shows the water rising and falling in the low section; the fix, while the slab is open, is to re-lay that section. Bellied pipe explained shows the picture.
Venting and the stack
The camera cannot see the vent, but a push up the stack from the basement, or down from the roof, shows whether the existing stack is sound where the new vent will tie in. Cast iron stacks rust through at the base; a new bathroom vented into one that is failing adds work later.
The lateral downstream
A basement bathroom adds fixtures to the lowest point in the house, which is exactly where a lateral backup arrives first. Camera the lateral to the main and check for roots, offsets and a surcharging main. If the line has a history, this is the moment to consider a backwater valve, which goes in while the floor is open. See inspection before a backwater valve.
Ejector pit considerations
If the design needs an ejector pit, the camera still matters: the pump discharges into the building drain or stack above the floor, and that connection point should be inspected and chosen from the footage. The pit itself needs a vent and a check valve, and the drain it discharges into needs to be clear enough to take the pump’s surge.
Permits and the plumber
A basement bathroom needs a permit almost everywhere, and the plumber will want to know the depth and route before quoting. Giving them the footage, the painted route and the depth marks shortens the design, sharpens the quote and avoids the change order that follows a surprise under the slab. See sewer permits and inspections.
After the work
Camera the new connection and the drain downstream before the slab is poured back, and again after, from the new cleanout the plumber should have installed. The footage shows the joints are tight, the slope is right and nothing was dropped into the line. Keep it with the permit.
What to record
The route painted on the floor with depths at each mark. The condition of the building drain with distances. The depth at the proposed connection and the gravity or ejector decision it drove. The lateral’s condition to the main. The after footage of the new connection. A buyer years later will want to know the basement bathroom was done properly, and this folder is the proof. See what a report should include.
Common questions
Do I need a camera inspection before a basement bathroom?
Yes. It finds the drain’s depth and route, which decide the design, and it finds defects that should be fixed while the slab is open.
How do I know if I need an ejector pit?
By the depth of the building drain at the connection point relative to the new fixtures. The camera and sonde find that depth; a plumber turns it into a decision.
Can the camera find the drain under the slab?
With a sonde and a receiver, yes, to within a few inches horizontally and an estimated depth.
Related guides
See inspection before finishing a basement, inspecting a basement floor drain, and sewer cameras for basement drains.