General Principles

The arrangement provided in a house or building, for collecting and conveying wastewater through drain pipes, by gravity, to join either a public sewer or a domestic septic tank, is termed as House Drainage or Building Drainage.

Aims of House Drainage

House Drainage is provided to –

• maintain healthy conditions in the building
• dispose off waste water as early and quickly as possible
• avoid the entry of foul gases from the sewer
• facilitate quick removal of foul matter
• collect and remove waste matters systematically

Principles of House Drainage

The following principles adopted for the efficient House Drainage system :

• The lavatory blocks should be so located that the length of drainage line is minimum.
• Drainage pipe should be laid by the side of the building rather than below the building.
• All the drains should be aligned straight between successive inspection chambers. Therefore, sharp bends and junctions should be avoided through chambers.
• The slope of the drains should be sufficient to develop self cleansing velocity.
• All the connections should be water tight.
• Drainage system should contain enough number of traps at suitable locations.
• The size of drain should be sufficient, so that flooding of the drain doesn’t take place while handling the maximum discharge.
• Rain water pipes should drain out rain water directly into the street gutters from where it is carried to the storm water drain.
• All the materials and fittings of drainage system should be hard, strong, resistant to corrosive action.
• Formation of air locks, siphon-age, under deposits etc. should be minimized.

Pipes

In a house drainage system, a pipe may have the following designations, depending upon the function it carries :

1. Soil Pipe – A soil pipe is a pipe through which human excreta flows.
2. Waste Pipe – It is a pipe which carries only the liquid waste. It doesn’t carry human excreta.
3. Vent Pipe – It is a pipe which is provided for the purpose of ventilation of the system. A vent pipe is open at top and bottom, to facilitate exit of foul gases. It is 1 m higher than the roof level.
4. Rain water Pipe – It is a pipe which carries only the rain water.
5. Anti-siphonage Pipe – It is a pipe which is installed in the house drainage to preserve the water seal of traps.

The following sizes of pipes are commonly used in House Drainage :

• Soil Pipe : 100 mm
• Waste Pipe : horizontal : 30 to 50 mm
• Waste Pipe : vertical : 75 mm
• Rain water Pipe : 75 mm
• Vent Pipe : 50 mm
• Anti-siphonage Pipe : Connecting soil pipe : 50 mm
• Anti-siphonage Pipe : Connecting waste pipe : 40 mm

Traps

A trap is a depressed or bent fitting which, when provided always remains full of water, thus maintaining a water seal. It prevents the passage of foul gases.

Characteristics of traps

1. It should be self cleansing.
2. It should be of non-absorbent material.
3. Its internal and external surface should have smooth finishing, to avoid dirt from sticking to it.
4. It should be free from any inside projections, so that flow is not obstructed or retarded.
5. It should be cheap and readily available.

Classification of traps

(a) Classification according to shape

• P-Trap
• Q-Trap
• S-Trap

(b) Classification according to use

• Nahni or Floor Trap
• Gully Trap
• Intercepting Trap

P-Trap

This resembles the shape of letter P, in which the legs are at right angles to each other.

Q-Trap

Also known as half-S-trap. This resembles the shape of letter Q, in which two legs meet at an angle other than a right angle.

S-Trap

This resembles the shape of letter S, in which both the legs are parallel to each other, discharging in the same direction.

Nahni or Floor Trap

It is used to collect wash water from floors, kitchens, bathrooms. It is made up of cast iron, with gravity at top to exclude big size solid matter. The cover can be removed to do frequent cleaning of the traps. It has small water seal.

Gully Trap

This trap disconnect sullage drain (collected from baths, kitchens etc.) from the main drainage system.It is made up of stone-ware / cast iron. Stone-ware trap is square in shape and cast iron is circular. It may have P-Trap or S-Trap. Gully trap is provided at the external face of a wall; which serve 2 or 3 connections from nahni traps.

Intercepting Trap

Intercepting trap is a special type of trap provided at the junction of house drain with public sewer. It has deep water seal of 100 mm, so prevents the entry of foul gases from public sewer line into the house drains. It has opening at the top for frequent cleaning, termed as cleaning eye / rodding arm.

Sanitary Fittings in House Drainage

The following fittings are commonly used in buildings, for efficient collection and removal of wastewater from the House Drainage –

1. Wash Basins
2. Sinks
3. Bath Tubs
4. Water Closets
5. Urinals
6. Flushing Cisterns

1. Wash Basin

Wash basins usually made up of pottery or porcelain ware. It is oval in shape as bowl, with an overflow slot at the top.

2. Sink

While wash basin used for washing face, hands etc. A sink therefore used in kitchen or lab.

3. Bath Tub

Its made up of iron or steel coated with porcelain or plastic material.

4. Water Closets

Water closet designed to receive and discharge human excreta directly from the person using it. It is of three types –

• Indian type
• European type
• Anglo-Indian type

5. Urinals

Urinals are of two types –

• Bowl type
• Slab or Stall type

The Bowl type used in residential buildings while Slab or Stall type used in public buildings.

6. Flushing Cisterns

Flushing Cistern used for flushing out water closets and urinals.

• Valveless siphonic type
• Valve fitted siphonic type

Most commonly used with Indian type is Bell Type Flushing Cistern, is the example of valveless siphonic type flushing cistern.