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Main Dewer Drains

A home's main sewer drain carries all household sewage to municipal sewer lines or to an on-site septic system. Older drains can become invaded by tree roots, causing blockage that can lead to sewage backing up into the house. Replacing a drain can be expensive, though newer techniques can lessen the amount of digging required.
How drain lines work

JUPITER FLORIDA PLUMBER
This graphic shows the basic paths of a typical home's sewer lines -- key parts of which carry no water at all, but only air to provide proper venting.

(1) All drain pipes should be connected to a network of ventilation pipes that go up through the roof. Venting prevents sewer gases from drifting out of drains into living quarters.  When having a JUPITER home inspected before making a purchase offer, make sure the inspector confirms that all venting pipes are present.

(2) Most plumbing fixtures have curved "trap" sections that hold a little water forming an airtight seal to keep gases in. This section of pipe is easily removed to clear clogs.

(3) Toilets also have a trap, which is what keeps standing water in the bowl. The toilet drain is the largest drain pipe in the house.

(4) All household drains meet below the house in a main drain that carries the wastewater to the municipal sewer lines or to a septic system. A Y-shaped pipe in a basement or crawlspace provides clean-out access. 

Sanitary vs. storm sewers

There are two types of sewer systems – storm water systems and sanitary sewers. Storm water systems or drains carry rainwater, ground water and road runoff water to an open body of water, such as streams, lakes and oceans. Sanitary sewers, however, carry wastewater from residential and commercial buildings to a treatment plant where the contaminants in the water can be removed.

Since the 1930s, storm drains and sanitary drains have been installed separately to prevent cross contamination. In a residence, the home's drain system is connected to the city sewer by an underground pipe called a lateral line, usually 4 to 6 inches in diameter, installed at a slope to use gravity for water flow.

The size of the home's drain piping is determined by the amount of flow possible and the type of waste material anticipated. For example, a bathroom sink usually has low volume and little if any solids in the water. These pipes are normally 1 ¼ inches in diameter. Bathtub, washing machine and kitchen sink drains carry larger volumes, with food and other solids possible in the kitchen sink. Therefore, a larger diameter pipe is necessary, usually 1 ½ inches in diameter.

Any plumbing beneath the house is large enough to accept the flow from the fixture drains. A 2-inch diameter pipe is common. All of these drains flow into the toilet drain to exit the building, so the toilet drain is the largest and matches the lateral line going to the city sewer system.

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