Rainwater Tank Pump System: Pressure Tank, Switch, and Flooded Suction

1,000-gallon rain tank at ground level under deck. Pump to supply hose (now) and drip (future). 10-ft lift, 100-ft run. Owner thinks ¾ HP self-priming centrifugal, pressure switch, no tank.

Pressure Tank Is Required

Without a tank, the pump cycles on/off for every drop of water—destroying the motor and wasting electricity. A tank provides 1–2 minutes of drawdown before pump starts.

Better Design: Flooded Suction

• Install pump at or below tank bottom level.
• Add a bung port (bulkhead fitting) at tank bottom.
• Water gravity-feeds pump inlet—no priming needed, higher efficiency, no suction leaks.
• Standard centrifugal pump (non-self-priming) works fine.

Components

• Pressure tank + switch: 20/40 or 30/50 PSI settings.
• Low-water cutoff: Float switch (sump-pump style) to stop pump if tank empties.
• Suction pipe: Same diameter as pump inlet.

Source for Bung Fittings

Farm/agricultural supply stores (tank fittings for liquid storage).