Plumbing System: Operation of Single Fall and Separate Falls


– What is the purpose of the fall?

– How the single chute works

– Separate chute operation

– Installation of a single or separate chute

The fall is the wastewater (black water and grey water) evacuation column. It can be unique or separate; each solution has its advantages and disadvantages. This post tells you everything.

What is the purpose of the chute?

In the form of a large-diameter vertical drain made of PVC, cast iron, or fibrocement, the chute serves one or more floors. It must allow the rapid evacuation of wastewater without stagnation or backflow.

This wastewater is of two types:

– black water that comes only from the WC;

– greywater coming from domestic activities in the kitchen and bathroom (sink, washbasin, shower, bathtub, dishwasher, washing machine, etc.).

Rainwater is discharged separately via downspouts.

Operation of the single chute


As its name suggests, the single fall evacuates all wastewater, i.e., black water and grey water, ending up in a collective network.

The tubes that make up the single chute must withstand high temperatures, as water from cooking or washing machines is particularly hot. Their diameter must be at least 100 mm. Their core, i.e., the inner wall, also has helical ribs designed to set the water in rotation and create an air tube, thus avoiding de-phonation, responsible for bad smells and noise.


One of the disadvantages of the single fall is that black water can still drain from the sink or shower, for example, since the toilet drains between 3 and 6 liters of water.

Operation of the separate waterfall



A separate chute is the most common. Blackwater and greywater are then discharged via different pipes. The black water flows through a grease trap before reaching the all-water tank, whereas the greywater flows directly to the all-water tank.

The tubes that make up the black waterfall are generally between 90 and 100 mm in diameter and between 50 and 80 mm for greywater. Their inner wall must be smooth to optimize the waterfall.


One of the disadvantages of the separate chute is the amount of work involved since a double network has to be installed.

Installation of a single or separate chute


The realization of evacuation networks must respect many strict rules and comply with departmental health regulations.

If it is possible to carry out this work yourself, it is better to call upon a professional who will guarantee an entirely compliant installation. 

Note: if the installation is not there, it will be imposed by the local authorities.


The connection diameter must correspond to the type of device to be connected. At the top, the chute is extended towards the roof by a vent pipe of the same diameter and capped with a vent cap to ventilate the tubes and facilitate drainage. At the bottom, the chute ends with a slope of 3 to 5 cm per meter so that the wastewater does not stagnate before reaching either a sewer or an individual sewerage system.

Do you need help?

JOE COLE PLUMBING is a full, 24/7 emergency service, Plumbing Contractor offering services in Residential, Commercial, and Industrial applications. They serve all of Broward, Miami-Dade, and Palm Beach counties.

Should you wish to read on something more specific, please do not hesitate to jot down your comments below and remember to share this post.

Read more on plumbing here:

Plumbing System: Operation of Single Fall and Separate Falls

Leave a Reply

Your email address will not be published. Required fields are marked *