How to Install a Slimline Rainwater Tank
Installing a slimline rainwater tank requires a flat, level base, a connection to a roof downpipe, and an overflow outlet directed to stormwater or garden. Most residential installations can be completed in under an hour without specialist tools or trade qualifications. No council approval is needed in NSW for tanks under 10,000 litres at ground level.
What You’ll Need
Before you pick up or take delivery of your tank, make sure you have the following sorted. A little preparation saves a lot of hassle on the day.
Tools & Materials
Spirit level, tape measure, adjustable spanner or pliers
Garden hose or downpipe adapter, PVC pipe and fittings for overflow
Silicone sealant or thread tape
For base from scratch: shovel, compactor, crushed rock, timber or concrete edging
Access
Measure your path from the street or garage to the install location. The tank is 700mm wide and 2 metres tall – fits through most side gates and passages. At 20kg empty, one person can carry it.
Placement
Choose a location as close to a downpipe as possible. The shorter the run between downpipe and tank inlet, the simpler the install. Think about where the overflow will go – ideally to a garden bed, lawn, or existing stormwater drain. Make sure the location won’t block access to meters, taps, or paths.
Build a Proper Base
A solid, level base is the single most important part of installation. A full 1,000 litre tank holds one tonne of water. If the base is uneven or unstable, the tank will lean, stress unevenly, and eventually fail.
Don’t: Never place a full tank directly on bare soil, grass, timber decking, or any surface that can shift, rot, or compress. Even if it looks level today, the weight will cause sinking and tilting on soft ground.
Place and Level the Tank
With the base prepared, carry or wheel the tank into position. At 20kg empty, this is a one-person job. Set it on the base and check with a spirit level across the top in both directions. Adjust the base material if needed before filling.
Leave clearance behind and around the tank for inlet, outlet, and overflow connections. Leave enough room for future maintenance or connecting additional tanks.
Multiple tanks: Place all tanks on the base before connecting. Align them so joining fittings line up cleanly. Leave a 20-30mm gap between tanks for the connection hardware.
Capture the Water
The tank needs a feed from your roof via a downpipe. There are two main ways to connect.
First-flush diverter: Catches the first 20-40 litres of each rain event – the dirtiest water with dust, pollen, and debris. Strongly recommended if using water for drinking or cooking. Optional for garden and toilet use only.
Set Up the Overflow
Every tank needs an overflow outlet. When full, incoming water has to go somewhere. Without a properly connected overflow, water will back up and cause pooling or damage around the base.
Connect the overflow fitting to your existing stormwater drain or direct it to a garden bed or lawn where water can absorb safely. Use PVC pipe at a slight downward gradient (minimum 1:100 fall).
Important: Make sure the overflow pipe outlet is not pointed at your neighbour’s property, your foundation, or any area where pooling could cause problems.
Multiple tanks: Only the last tank in the chain needs an overflow. Water fills the first tank, equalises across all connected tanks, and only overflows once the entire system is full.
How to Link Tanks Together
Every tank comes with all joining fittings included. Connecting multiple tanks is straightforward.
Position all tanks
Place them on the level base with a 20-30mm gap between each.
Locate the joining ports
Pre-fitted threaded outlets positioned near the base of each tank.
Connect adjacent tanks
Apply thread tape to all threaded connections. Hand-tighten, then a quarter turn with a spanner. Don’t overtighten – poly fittings crack under excessive force.
Connect downpipe & overflow
Feed your downpipe to the first tank. Connect the overflow to the last tank in the row.
How it works: Water enters the first tank, fills it, then flows through the joining connections into the next tank automatically. No pump needed between tanks. No limit on how many you can connect.
Fitting a Tap or Pump
For garden use, the simplest setup is a brass tap or ball valve fitted to the outlet at the base of the tank. This gives you gravity-fed flow directly into a hose or watering can.
A full 2 metre tall tank gives reasonable flow for hand watering and drip irrigation, but it won’t be mains pressure. For most garden use, this is perfectly adequate.
Tap tip: Fit the tap on the lowest outlet and keep it off the ground. A short stand or riser pipe keeps it clean, accessible, and prevents corrosion from sitting in dirt or mulch.
Ongoing Care
Slimline poly tanks are very low maintenance. A quick check once or twice a year keeps everything running properly.
Inlet screen: Clear leaves, debris, or sediment. A blocked screen reduces flow and causes downpipe backup in heavy rain.
Overflow: Check the pipe is clear and draining freely. Not blocked by soil, mulch, or garden growth.
Gutters: Keep roof gutters clean. Cleaner water off the roof means less tank maintenance. Gutter guard mesh helps significantly.
Tap & fittings: Check for drips or weeping. Tighten gently if needed. Replace washers if a tap starts dripping.
Mosquitoes: Ensure all openings are screened with mesh. If screens are intact with no gaps, mosquitoes can’t get in.
Sediment: Fine sediment accumulates over years. Drain and rinse with a hose every 5-10 years if you notice discolouration or reduced flow.
What Not to Do
⚠️ Skipping the base
A full tank holds one tonne. Grass, soft soil, or uneven ground leads to tilting, stress cracking, and failure. Build the base properly first.
⚠️ Forgetting the overflow
Every tank needs one. Without it, water backs up and overflows from the top during heavy rain, pooling around the base.
⚠️ Overtightening fittings
Poly fittings crack under excessive force. Hand-tight plus a quarter turn with a spanner is enough. Use thread tape if it leaks.
⚠️ No gutter connection
Water falling directly onto the tank from eaves creates noise and wear. Always connect via a downpipe or diverter.
⚠️ Blocked overflow outlet
Pointing it at a fence, retaining wall, or neighbour’s property causes problems. Direct to a garden bed or stormwater drain.
⚠️ DIY internal plumbing
Connecting rainwater to toilets, laundry, or hot water must be done by a licensed plumber to meet Australian plumbing standards and backflow prevention requirements.
Need a Hand?
Not sure about any part of the installation? Call us. With over 30 years in the rainwater tank industry, there’s not much we haven’t seen. Happy to talk through your setup, recommend the right number of tanks, or point you in the right direction.
Our 1,000 litre slimline rainwater tanks are $350 each, brand new with manufacturer’s warranty and all joining fittings included. Pick up from Lake Haven or St Marys. Delivery also available.