Your kitchen sink has backed up for a week straight. Here's what's really going on.

First test: is it the kitchen, or the whole house?

Run the bathroom sink and flush a toilet while you watch the kitchen sink and the lowest drain in the basement. Montgomery Township Municipal Sewer Authority's own troubleshooting page makes this the first check: if drains gurgle as they back up, that points at the main line rather than one fixture. Their page describes the test as running fixtures and watching whether water rises somewhere else.

• Only the kitchen sink is affected → the branch line serving that sink, usually within the house.

• Kitchen plus laundry tub, floor drain, or a downstairs toilet → the house drain or the lateral out to the street.

That distinction changes the work and the price. A branch line is $100 – $400. The main line is $200 – $700.

Why grease makes a clog that keeps coming back

Montgomery County's own disposal guidance puts it plainly: cooking oil and grease stick to pipes when poured down the drain and can cause backups, and flushing with hot water does not always clear it. Hot water and detergent move the grease a few feet down the pipe, where it cools and sticks again. That is exactly the pattern of a sink that works Monday and fails Wednesday.

A cable bores a hole through that build-up. Water runs, everyone relaxes, and the hole closes over. Stripping the pipe wall back to bare metal is a different job — that's what hydro jetting is for, at $600 – $1,600 — and it is usually worth it only when the line has repeatedly re-clogged in the same spot and a camera has shown the pipe is sound enough to take it.

Older houses here have two extra problems

Bucks County's housing stock is older than the newer subdivisions suggest: roughly a tenth predates 1940, another fifth went up in the 1940s and 1950s, and the largest single group was built between 1960 and 1979. Kitchen drains of that age are often cast iron or galvanized steel, and the inside diameter is smaller than the day it was installed.

The second problem is access. The sewer authority notes that a home built before 1978 may not have a sewer line cleanout at all. No cleanout means the plumber pulls a toilet or opens the line somewhere, which adds an hour before any cabling starts.

Outside, the same age shows up as roots. Mature trees on an older property can send roots into the underground pipe and cause the backup, which is the case the authority describes.

Who owns the pipe that's blocked

In Montgomery Township, the authority is direct about it: in most cases the property owner is responsible for maintaining, repairing and replacing the entire service line from the building to the connection at the public sewer main. Blockages, that same authority notes, can happen either in its main or in the private line the owner maintains — so if several houses on your block are having trouble at once, report it before you pay for a camera.

In Philadelphia the rule is the same in effect: the city lists maintaining and repairing the sanitary and storm sewer lateral connecting your house to the sewer main as a customer responsibility.

Philadelphia row homes also have two parts most suburban homes don't. The Water Department's responsibility list includes a curb trap — a J-pipe between the house drain and the lateral — and a fresh air inlet vent pipe. The curb trap is a classic place for a kitchen-grease blockage to settle, and it is on the homeowner's side of the line. If the city finds lines that aren't fully operational, it serves a notice of defect with a period to repair.

On septic? A kitchen backup may not be a clog at all

Much of upper Bucks and parts of Montgomery County are on on-lot systems. The state lists backup of sewage into laundry tubs or other fixtures among the signs of a system in trouble, and recommends pumping the tank every three years or so depending on tank and household size. If your last pump-out is a hazy memory, get that date before anyone runs a cable.

The same state guidance says the bacteria doing the work in the tank can be impaired by substances put into the system, listing oils and grease and harsh drain cleaners among them, and advises using the garbage disposal sparingly because those wastes add to the burden.

About the bottle under the sink

If you've already poured chemical drain opener down a line that isn't moving, tell whoever opens the trap, because it's still sitting there. Leftovers don't go in the trash: Bucks County accepts caustics such as household lye and oven cleaner at its household hazardous waste collection events, which are free drop-off with no registration.

Permits, and when you actually need one

Clearing a stoppage is not permit work in Philadelphia — the city's plumbing permit page specifically exempts stopping leaks and clearing stoppages, while installation, alteration, replacement and repair do need a permit. If the fix turns into pipe, the city allows some of that work through an EZ permit with no plans, including a new or replacement house drain serving a single building, and sealing a lateral.

In Bucks and Montgomery counties there is no single permit desk. The state code sets the floor but over 90% of Pennsylvania's 2,562 municipalities administer and enforce it themselves, and every municipality in Bucks County has opted in, so the form, the fee and the inspection slot come from your own township or borough.

Where a line has to be dug up or relined, you're into $2,500 – $8,000, and a full replacement is $5,000 – $15,000. Replacing a failed disposal, trap arm or basket strainer as part of the same visit sits at $300 – $1,200.

Selling, or just bought, in Lower Bucks?

Some townships require the lateral to be looked at when the property changes hands. Falls Township requires a video inspection of the sanitary sewer lateral from the residence to the connection, prior to transfer, and its ordinance says the purpose includes finding holes or damage, checking cleanout caps, and identifying clay or older laterals. If the line is found defective, the ordinance puts replacement or realignment at the owner's expense, performed by a master plumber or utility contractor. Check your own township's code before you assume you're exempt.

What a sensible visit looks like

• Cable the line through the nearest cleanout, correct cutter head for the pipe size.

• If it clears and has cleared before, run a camera. The authority describes the same order: auger first, then a fiber optic camera to work out what's going on.

• Get the recording and the footage distance, in feet from the access point. That number is what tells you whether the next step is jetting, a spot repair or nothing.

• Ask what was pulled out. Grease, roots and a broken pipe are three different futures.

Before signing anything, check the contractor's Pennsylvania home improvement registration on the Attorney General's public register, and note that a contract above the state's threshold gives you three days to cancel. In Philadelphia, plumbing work also requires the contractor to hold the city's own trade licence, and the city publishes a lookup. HomeProjectMatch introduces you to independent local contractors; we don't screen them, so those two checks are yours to make.