If the bathtub fills with water when the toilet flushes, or the tub and toilet back up at the same time, the blockage is downstream of both of them. The two fixtures don't share a trap, so there's no clog in either one that could cause it. The water is backing up from a pipe they both drain into: the bathroom's branch line, or more often, the main line that carries everything out to the street.
Why the tub is where it shows up
Every fixture in the house drains through its own trap into a branch line, the branches join the building drain under the house, and the building drain leaves through the sewer lateral to the public main. When the pipe is blocked somewhere below a group of fixtures, water from upstream has nowhere to go but back up, and it comes out of the lowest opening it can reach.
In most single-story Burbank, Glendale and Valley homes, that lowest opening is the tub or shower drain. It sits a few inches above the floor, lower than the toilet bowl's rim or the sink. A toilet flush also sends a lot of water down at once, so it's usually the flush that pushes the backup into the tub, not the tub filling on its own.
Branch line or main line? Run the house test
Before you call, a two-minute check narrows it down. Flush the toilet once (not repeatedly) while someone watches the tub, then try the other fixtures one at a time, keeping the water use small.
| What you see | Where the blockage usually is |
|---|---|
| Tub fills when this toilet flushes; the kitchen sink and the other bathroom drain fine | The branch line serving that bathroom |
| The tub or shower in another bathroom fills when you flush, or run the washer | The building drain or main line, below where the bathrooms join |
| Kitchen sink, washer and toilets are all slow or gurgling | The main line |
| Water comes up at the cleanout outside when you open it | The main line between the cleanout and the street |
| The cleanout is dry when you open it, but the tub still backs up | Inside the house, upstream of the cleanout |
| Neighbors are backing up at the same time | Possibly the public sewer main; report it to the city |
Gurgling without a full backup follows the same logic. Our page on what gurgling drains mean walks through the cross-fixture test in more detail.
What to do first
- Stop all water use. Tell everyone not to flush, shower or run the dishwasher or washing machine. Every gallon that goes in comes out of the tub.
- Don't keep plunging the toilet. If the clog is past the toilet, the plunger only pushes dirty water out of the tub drain. One or two tries is the limit.
- Skip the drain cleaner. Chemicals won't reach or dissolve a main line blockage. They sit in the tub water and make it caustic for you and for whoever clears the line.
- Find the cleanout. It's usually a capped pipe outside near the foundation, or where the line leaves the house. See how to find your sewer cleanout. Wearing gloves and eye protection, stand to the side and loosen the cap slowly. If water drains out there, letting it spill outside is far better than inside.
- Keep people and pets away from the water, and photograph any damage before cleanup.
- Call a plumber to clear the line from the cleanout and find out why it blocked.
If sewage is already on the floor, our main sewer line backup guide covers the emergency steps, safe cleanup and insurance photos in order.
What usually blocks the main line
LA Sanitation says over 50% of sewer backups are caused by tree roots and fats, oils and grease. Roots get in through cracks and joints in older clay and cast iron laterals, which are common under 1940s to 1960s Valley homes, and they catch everything else that comes down the line. Wipes labeled "flushable," paper towels and grease poured down the kitchen sink add to it. A line with a sag (a "belly") holds water and debris and tends to block again in the same spot.
That's why a main line that has backed up once deserves a camera look after it's cleared. If it keeps happening, read why a main line keeps backing up, tree roots in your sewer line and what not to flush.
Whose pipe is it?
In the City of Los Angeles, LA Sanitation says property owners are responsible for maintaining and repairing their entire private sewer lateral, from the building all the way to the connection in the street. Burbank's Public Works department says the same: property owners maintain the sewer lateral that connects the building to the city's sewer main, and the city asks residents to report overflows that appear to come from the city's mainline to Public Works at (818) 238-3915 during business hours or (818) 238-3778 after hours. In LA, LA Sanitation's 24-hour line is 1-800-773-2489.
Burbank also runs a sewer lateral rebate program. Its SLURP FAQ says the typical cost to clean and video record a lateral is $300 to $700, that a $150 rebate requires a video recording after cleaning, and that a cleanout, while not required, is recommended for every property, at a typical cost of $300 to $500 to install.
How a plumber clears it
The fastest, cleanest way in is the cleanout. California's plumbing code (section 707.4) calls for a cleanout at the upper end of each horizontal drain, and allows a two-way cleanout near where the building drain meets the sewer, extended to grade outside. Many older homes in the area were built without one. Without a cleanout, clearing the line usually means pulling a toilet and running the cable through the toilet flange, which takes longer and is messier. If that's your house, ask about sewer cleanout installation; it makes every future visit faster.
Once the line flows again, a sewer camera inspection shows what caused it: roots at a joint, a belly, a crack or a grease buildup. That tells you whether a cleaning will hold or the pipe needs a repair.
What clearing a main line costs in LA
These are published ranges from other LA-area plumbers and cost guides. They're a sanity check, not a quote.
| Job | Published range | Source |
|---|---|---|
| Main line cleaning, Los Angeles | $250–$1,000 | Angi (Los Angeles) |
| Main sewer line, Glendale & Burbank | $250–$600 | Alpha-Beta Plumbing (cost guide) |
| Main line (cable), San Fernando Valley | $225–$495 | Last Drop Plumbing & Rooter |
| Main sewer line through an existing cleanout, SFV | $150–$400 | BBC Rooter & Plumbing |
| Main sewer snaking, Los Angeles | $250–$400 | Expertise Plumbing |
| Lateral cleaning plus video, Burbank | $300–$700 | City of Burbank (SLURP FAQ) |
At Rooter Pros, a backed-up main line gets a free estimate: call (818) 669-9019 and you get the price before any work begins, with flat-rate pricing and no overtime charges, day or night. New customers can also ask about our $49 first-time drain cleaning coupon: one clogged drain or line cleared, new customers only, residential, Monday–Friday 7am–5pm, through an accessible ground-level cleanout, not valid with other offers. It's a new-customer special, not our regular rate. Seniors, active military and veterans get 10% off; mention it when you call. See our pricing page and the drain cleaning cost guide for more.
When to call a plumber
Call right away if the tub fills when the toilet flushes, if more than one bathroom or the kitchen is affected, if water comes up at the cleanout, or if sewage is on the floor. Call too if it's the second backup in a year, since that usually means roots, a belly or a break that will keep causing it. If only one bathroom is involved and it cleared on its own, it's still worth having the branch line cleaned before it happens on a weekend.
Tub and toilet backing up in Burbank, Glendale or the Valley? Rooter Pros clears the line from the cleanout and shows you what caused it. Licensed & bonded (CSLB #917630), open 24/7, with free estimates, flat-rate pricing and no overtime charges.
Call (818) 669-9019Prices in the table are typical published ranges from other Los Angeles-area plumbers, cost guides and the City of Burbank as of October 2026. They are not Rooter Pros quotes and change over time. The code section is from the 2025 California Plumbing Code as published online, and city responsibilities and phone numbers are from LA Sanitation and the City of Burbank's published pages; your city has the final word. Sources are linked above.