The basics on drainage system comprises of waste water from the bathroom, toilet, kitchen, laundry rooms draining into main council sewer or septic tank, with help of PVC pipes.
Without proper drainage system, a house cannot be habitable. Drainage pipework in a house starts at the substructure level of building a house; most of the pipes are installed inside the ground slab.
A bathroom that has a toilet, a shower, wash hand basin, bathtub or Jacuzzi, should have the drainage pipe passing in the ground slab. The water closet (toilet) should have a four-inch pipe, place with right angle bend to take away the sewer out of the house into the inspection chamber and discharge to main sewer or septic tank. The bathroom should have floor trap for draining water on the floor away into main sewer line.
Note that balconies and kitchen on upper floors should have floor traps on their floor this helps in draining water from these rooms down to ground floor. Instead of having ugly pipes protruding outside the slab draining water directly to ground floor. Remember in a building with more the one floor, except for water closet, all other drainage pipes is installed inside the concrete. So a lot of keenness by plumber is demanded to avoid leakage in the slab.
Toilets on upper floor are connected to four-inch pipe above the slab, which with the help of four-inch down pipe, takes the waste down the ground. It’s important to remember that the sewer pipe from upper floor and sewer waste from ground floor, use different pipes, but they can discharge the waste into the same inspection chamber. This helps to control waste in case of blockage on one of the pipe.
Below are other important factors taken into consideration in a drainage system.
- Planning. It’s important to plan well, before installing your drainage pipes. A layout plan, showing how the pipes will run on the floor is very important. You can have a qualified Plumber or Service Engineer, to design and draft for you the drainage plan.
- The plumber should be very skilled and with enough experience. You can ask your friends who have built before to recommend for you a good plumber. The plumber can also take you to his previous work. Get the contacts of the previous clients and call them to understand more about competence and behavior of plumber before you hire him.
- External Drainage. The invert level between the first inspection chamber and the main sewer or septic should be established early before foundation work, so that you don’t have a situation, where after completing your house, you realize that the invert level of inspection chamber on ground floor of your house is lower than the invert level of inlet of main sewer or septic, meaning the waste from main sewer line will drain into the house instead of the reverse. For buildings being built-in areas with existing council sewer lines, or existing septic tank, the invert levels must be taken before even start foundation work. The invert level of the main sewer line will determine how high the ground floor slab will be positioned, so that the waste can drain from the house, down into the main sewer.
- The adhesive Glue: The adhesive for sticking the pipes and their accessories should be of high quality, so that it bonds well, without allowing leakage. Locally TANGIT glue is widely accepted. Before applying the glue, the two surfaces must be clean and dry. Sometimes the surfaces are made rough by scratching using hacksaw blade, cleaned and glue applied, this helps in enhancing the bonding of the two surfaces.
- Pitch: Proper pitch/slope should be adopted. Pitch simply means the angle in which water will flow easily and gradually with the help of gravity. Every drain pipe, whether underground or in a wall, must have some type of pitch and be sloped properly to allow waste water leaving the home to drain out. To make sure water will drain properly and won’t back up in the line, a good rule of thumb to follow to get the pitch when installing external drain pipe is a drop of 3cm per every 100cm (which gives you 3% pitch) otherwise, a pitch of between 3% to 7% can be adopted, especially for pvc pipes. If the slope is very steep, then water will move very fast and leave the solid waste behind, if pitch is low, then the water and solid waste won’t move or it can even move in reverse direction.
- Inspection chamber. When placing the inspection chamber, make sure the minimum angle from one inspection chamber to another is 90 degrees, if you put less than 90 degrees the waste may not go smoothly.
Place inspection chamber at every turn of the pipe line.
Have a maximum of 10m distance between two inspections, to make it easy to unblock.
Use heavy gauge pipe for the entire drainage pipe.
- Concrete Surround: Drainage pipes passing under driveway or parking should have concrete surround. This is concrete poured over the drainage pipe to protect the drainage pipe from damage, as a result of pressure from the vehicle passing over it.
- The waste pipe passing below the parking or drive way, also need to be placed at least two feet from the ground level.
- Position of the Floor Trap. The floor trap should be place at one corner of the room, away from the bathroom door; this is so that you have one slope on the floor, from one side going down to the side where the floors trap is located. If the floor trap is put in the middle of room, then you will have the slope from all the four sides of the room coming down in the middle, creating something like a depression in the room. Placing the floor trap opposite the door, is to avoid the risk of bathroom water flowing out of bathroom into the adjacent room through the door, because the slope will be lower where the floor trap is located, hence the water on the floor will flow down the slope away from the door into the drainage sy
- Controlling Bad smell: Waste water from wash hand basin, from the floor should drain into either floor trap or into a gulley trap. This is a very important point, because the water held in the floor trap or gulley trap prevent bad smell in drainage from moving up the pipe and entering the room. Toilets have a built-in trap and that’s why after flushing the cistern there is always water remaining. Just like in waste water drain this toilet trap prevents bad smell from the sewer pipe entering the room.
- Inspection chamber cover can be concreted on site instead of buying the plastic covers that don’t last.
- Ventilation (Vent) pipe: The drainage system must have a vent pipe, which release toxic gasses from the drainage system into the atmosphere. The vent pipe should terminate above the roof. Without vent pipe the gases in the system can prevent waste water from flowing and even drain the water in the sinks. Because of the pressure of trapped in the drainage system without vent, bad smell from sewer will always be released into the house through the sinks and other openings.