800L 3P Technik Rain Tank System Review (2026):

800L 3P Technik Rain Tank System Review (2026): The Rainwater Harvesting Kit That Replaces Four Water Butts

What Is the 3P Technik Rain Tank System?

Most "water butts" are a barrel and a tap. This is a different category of product entirely: a complete rainwater harvesting system built around 3P Technik's flagship 800-litre Wall Tank — the model the German manufacturer positions for buyers who need high capacity in a minimal footprint. And that footprint really is the story: the tank stands 179cm tall but occupies just 80cm × 60cm of ground, a flat-backed slim column designed to sit tight against a house or garage wall next to a downpipe. Four standard 200L barrel butts would eat several times the floor space for the same stored water.

In the granite grey finish reviewed here, it reads more like a piece of contemporary garden architecture than a plastic tank — a genuine consideration when something this size lives permanently against your wall. Black and sandstone versions are also available at the same price.

What elevates the price to £989.99 is that this is the full system, not the bare tank. In the box:

• 800L Wall Tank — UV-stabilised polyethylene, sealed construction, 37kg empty
• 3P Technik Filter Collector — fits your downpipe, diverts rainwater into the tank while filtering out leaves and debris
• Waterproof submersible Garden Steel Pump — connects to the brass fittings at the tank base for pressurised watering around the garden
• Pump-to-tank connection kit and water level sight gauge
• Wall Tank fitting kit — wall fixing bracket, plastic hi-flow ¾" BSP tap, hole saw set and rubber grommets

The pump is the piece that changes how you'd actually use this. Gravity-fed water butts give you a dribble at a tap 30cm off the ground; a submersible steel pump gives you working pressure through a hose — enough to water borders, run a sprinkler on beds, or fill cans quickly at the far end of the garden. During a hosepipe ban, harvested rainwater delivered under pump pressure is about as close to normal watering as it gets, entirely legally.

Full Specifications

Capacity	800 litres (176 gallons), expandable with additional tanks
Tank dimensions (H×W×D)	179cm × 80cm × 60cm
Material	UV-stabilised polyethylene (PE), sealed construction, shot finish
Empty weight	37kg
Connections	3 × ¾" BSP brass threads (1 tap point ~30cm from ground; 2 interconnect/drain points near base) + 95mm plugged top opening
Pump	Waterproof submersible steel garden pump (included)
Filtration	3P Technik Filter Collector (downpipe-mounted, included)
Colour	Granite grey (also in black and sandstone)
Manufacturer	3P Technik - made in Germany
Price	£989.99 (Water Butts Direct, July 2026)

Key Features Worth Your Attention

💧 Filter Collector: Set-and-Forget Rainwater Capture

The included Filter Collector is what separates a proper harvesting system from a butt with a diverter. It mounts on your downpipe, maximises the rainwater diverted into the tank, and screens out leaves and debris before they ever reach the water. That matters over years of ownership: debris is what turns stored rainwater stagnant and clogs pumps. Cleaner water in means less maintenance and a healthier pump.

⚙️ Submersible Steel Pump: Real Watering Pressure

The waterproof steel pump hooks up to the brass connectors at the base of the tank, drawing on the full capacity of the system — including any additional tanks you link on later. This is the difference between "storing rainwater" and "using rainwater like mains water": pressurised flow through a hose, all around the garden.

🔗 Expandable: Grow to 1600L or 2400L

The base tank has interconnection points with metal-threaded connectors, so you can add further 800L tanks in a row along the wall as your needs grow — one pump serves the combined capacity. Water Butts Direct sells pre-configured 1600L and 2400L versions of the same system if you'd rather start big (see comparison below).

🧱 Built for Permanence

UV-stabilised polyethylene with a sealed construction, brass ¾" BSP fittings rather than push-fit plastic, and a wall fixing bracket included for securing the tall profile. 3P Technik supplies the professional horticultural market as well as domestic buyers, and the fittings specification reflects that.

Pros & Cons

Which Size System? 800L vs 1600L vs 2400L

System	Capacity	Price	Cost per Litre	Best For
800L Rain Tank System ⭐	800L (1 tank)	£989.99	£1.24	Typical gardens, first-time harvesters
1600L Rain Tank System	1600L (2 tanks)	£1,417.99	£0.89	Large gardens, greenhouses, allotments
2400L Rain Tank System	2400L (3 tanks)	£1,942.99	£0.81	Smallholdings, schools, commercial sites

Prices from Water Butts Direct, July 2026. Exploring smaller or cheaper options? See our full water butt guides and reviews.

The per-litre economics improve as you scale — the second and third tanks share one pump and one filter — but the 800L base system is the right entry point for most households. It's expandable later, so you're not locked into your first decision: start with one tank, add another if you find yourself running dry in July.

Who Should Buy the 800L 3P Technik Rain Tank System?

✔ Buy it if: you're a serious gardener on a water meter, you've outgrown standard water butts, or you live in a region where summer hosepipe restrictions keep biting. It also makes strong sense for greenhouse growers and anyone with extensive borders or raised beds — plants generally prefer rainwater to treated tap water anyway, particularly ericaceous species like rhododendrons, camellias and blueberries.

✘ Skip it if: you have a small patio garden where a couple of containers need watering — a standard 200–300L butt at a tenth of the price will serve you fine. Renters should also think twice: this is a semi-permanent installation involving downpipe modification and wall fixing.

Our Verdict: 4.5/5

Judged as a water butt, £989.99 looks steep. Judged as what it actually is — a complete, expandable rainwater harvesting system with filtration, pumped delivery and professional-grade fittings — it's coherent value, and buying the components separately would close much of the gap while leaving you to solve the integration yourself. The slim wall-tank format is the cleverest part of the design: 800 litres of storage in the dead space beside a downpipe that most gardens waste.

With UK water bills climbing and metered households now the majority, the payback case gets a little stronger every year — and the garden keeps drinking through every hosepipe ban. For committed gardeners, this is the point where rainwater harvesting stops being a gesture and starts being infrastructure.