Know Your Plumbing System

Every house has two plumbing systems that never meet. The supply side brings clean water in under pressure; the drain side carries waste out by gravity and lets air in through the roof. Knowing where each part sits makes it easier to describe a problem, to shut the water off in a hurry, and to tell an annoyance from a fault that is doing damage.

Clean Water Under Pressure

The water service, a single pipe from the city main under the street, comes through the basement wall or floor, usually on the street side of the house. The main shutoff valve and the water meter sit close by. In an older house the main is often a gate valve with a round handle; newer work uses a quarter-turn ball valve, which is easier to close in a hurry.

Past the meter, the cold line divides. One branch runs to the water heater’s cold inlet, which has a valve of its own, and the rest feed the cold side of every fixture. Hot water leaves the top of the heater and travels beside the cold line to the sinks, tubs, showers and appliances; toilets take cold water only. Under a sink or behind a toilet, a small fixture stop shuts off that one fixture without closing the whole house. Supply pipe in older houses is often galvanized steel, later copper, and in recent work PEX; a leak or corrosion in any of them is a matter for pipe repair.

Gravity, Water Seals and Air

The drain side works without pressure, so every pipe in it has to slope. Each fixture empties through a trap, the U-shaped bend under a sink or tub, cast into the base of a toilet or set below a floor drain grate, which holds a few inches of water as a seal against sewer gas.

Branch drains slope from the traps to the stack, the large vertical pipe that runs through the house. Its top continues up through the roof as the vent, which lets air in behind draining water so that traps keep their seals and drains run quietly. At the bottom, the stack turns into the building drain, often under the basement floor in an older house, which also takes the floor drain and the laundry. A capped main cleanout gives access to the line, and the building drain leaves through the foundation as the lateral, which runs under the yard to the city sewer. A clog anywhere along that path is cleared by drain cleaning.

How the Parts Wear in an Older House

In Youngstown, where many houses were built before the Second World War, a house may still have most of its original parts, and each of them fails in its own way.

How each part tends to fail in an older house

Part	Often found	How it fails
Main shutoff	Gate valve with a round handle	Seizes, or no longer closes fully after years without use
Supply pipes	Galvanized steel	Rusts inside until the pressure drops and the water runs brown; leaks at threaded joints
Fixture stops	Multi-turn compression valves	Drip at the stem when turned, or will not shut off
Water heater	Gas or electric tank in the basement	Fills with sediment, rusts through at the bottom, or the relief valve weeps
Traps	Metal traps under sinks, drum traps under old tubs	Clog with hair and grease; old metal corrodes thin
Stack and building drain	Cast iron	Cracks along the bottom, or rusts through near the base of the stack
Floor drain	Cast iron with a trap below the grate	Trap dries out and lets in sewer gas; backs up when the main is blocked
Lateral	Clay tile in short sections	Roots enter at the joints; sections shift, sag or crack
Roof vent	Cast iron or galvanized pipe through the roof	Blocked by leaves, a nest or frost, so drains gurgle and slow

Most of these failures show themselves first as a symptom, such as a slow drain, a gurgle or a smell, and reading those symptoms narrows down where to look before anything is opened.