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RotoTank ™, First Flush system, harvesting water


RotoTankTM manufactures the First Flush System, including water tanks, chemical tanks, transport tanks, septic tanks and silos. We are a national brand with branches around the country. We sell directly to the public and deliver for free.







RotoTank™ First Flush System

RotoTank™ First Flush System Downloads

50l 500mm 250mm 512mm Download

RotoTank™ First flush systems are a critical part of your rainwater harvesting system, First Flush systems help to divert the sediment filled water to a holding tank, RotoTank™ specially designed a 50l tank for this purpose.

RotoTank ™ First Flush System

As the tank fills, the sediment settles at the base of the tank, the tank has been designed to allow the sediment to settle down to a pivotal point where a fitting can then be connected to the supplied tap at which point you can then connect a hose pipe. As the water rises in the tank the sediment settles, the clean water diverts to your rainwater harvesting tank and you prevent these contaminants from going into your system.

Why is RotoTank™ the best First Flush System on the Market in South Africa?

The design is easy to install, the 50l capacity tank is the largest first flush on the South African market and allows you to collect the most amount of sediment and assists to keep your tank free of leaves and pests, the unit comes supplied with rubbers to prevent rodents and other small creatures or insects from entering your tank.

What do you receive with your First flush system?

Benefits of the RotoTank™ Rainwater Filter System

  • RotoTank™ 50l wall mounted tank
  • Comes in a range of colors to match your tank
  • PVC Gutter buddy – leaf catcher
  • 40/20mm reducing bush
  • Plastic tap
  • Rubber seals
  • Specially designed easy empty 50l tank
  • Easy to Install
  • Prevents leaves and dust from entering your tank
  • Keeps out rodents and other insects and pests
  • Extends the life of your pumps and filters
  • Healthier cleaner water in your rainwater harvesting tank

An Alternative system, RotoTank™
First Flush Down pipe kit.

RotoTank rainwater tank recommended pipe sections for installation

The full kit is available with our Online Rainwater Harvesting Combos.

The system can be set up in several ways to suit your wall and gutter pipes.

What is a RotoTank™ Rainwater Filter System?

The First Flush rainwater filter system will divert any small or dissolved pollutants from your roof and gutters into a separate pipe chamber, so it does not enter the tank.

It is best to have one first flush system on each downpipe. However, a single unit can be placed close to the tank and perform a first flush for several downpipes. This will really depend on how big your roof catchment is and how clean you need the water to be.

The first flush system is a simple and effective device. After the rain, just drain the system through the valve, ready for the next rain. The bottom of the unit (end cap) can be screwed off to fully clean the unit occasionally. During periods of frequent rain, it may not be necessary to drain the first flush device every time it starts raining as the roof and gutters may already be clean.

First flush systems work best when a leaf catcher box is installed at the start of the down pipe. The leaf catcher box is fitted at the start of the downpipe either directly on the underside of the roof gutter at the facia board, or to the wall. The device deflects leaves and debris away from the flow of rainwater. 

It also stops sediment building up in the bottom of your tank.

When it first starts to rain, water slowly builds up in the roof gutter system before it exits through the downpipe.

The first flush of water from the roof can contain amounts of bacteria from decomposed insects, lizards, bird, and animal droppings and concentrated tannic acid. It may also contain sediments, water borne heavy metals and chemical residues, all of which are undesirable elements to have in a water storage system.

Gutter mesh and baskets (leaf catchers) will help with leaves and larger debris but can’t stop small bits like dust and bacteria. That is why it is recommended that you install a First Flush System.

We all know that prevention is better than cure and so it makes sense to stop the pollutants from entering your tank.


How it works: The first flush device is installed along the gutter down pipe that will feed into your water tank. As the water level in the first flush chamber (110mm pipe) rises, the ball floats and rises.

Once the chamber is full, the ball rests on a seat inside the chamber preventing any further water entering. The subsequent flow of clean water is then automatically directed along the pipe system through the T piece into your RotoTank rainwater tank.


You will need to secure the First Flush and pipes to a wall or other structure. This should only be done after you have assembled the first flush kit in full as follows:

1) Take the 650mm x 110mm PVC pipe to use as the chamber pipe. The length you require should leave enough area at the bottom of the device to the ground as space is required for the end cap to be screwed off for occasional cleaning.

2) Attach the bottom end base cap assembly to the 110mm pipe you have cut using PVC plumbing glue or a good plumbing silicone. HINT: Only screw the valve into to the end base cap once the installation is complete. This will minimize the chance of snapping the valve off in the end cap housing if you drop the pipe while installing!

3) Insert the ball into the chamber.

4) Insert the top end cap onto the 110mm pipe and secure using PVC glue. (The top cap has a belled 80mm inlet).

5) Once the unit is assembled and the PVC glue is dry, remove or cut the existing downpipe at the required height.

6) To affix the first flush unit to the wall, a 110mm mounting bracket is included in the DIY kit. (If more mounting brackets are required to secure the unit, they can be bought at your local branch)

7) Supplied 400mm of 80mm pipe, can be inserted into the T- piece and the base section, you can know attach to the correct position on the wall.

8) Place the gutter buddy in position screw into the wall, then attach your first flush system below.

9) The T piece supplied should still follow a fall to the tank.

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