A buffer tank is the single upgrade that turns a pressure washing rig from a hose-dependent operation into a fully independent business. Without a buffer, you're at the mercy of whatever water pressure and flow rate the customer's outdoor spigot provides — and residential hose bibs routinely deliver only 3–5 GPM. Most commercial pressure washers demand 4–8 GPM or more. The math doesn't work without a tank in between.
This guide covers everything: why you need a buffer tank, how to size it correctly, how to plumb a gravity-feed setup, and what tanks actually work well in a commercial pressure washing context.
Why Pressure Washers Need a Buffer Tank
A pressure washer's pump is a positive displacement pump — it pulls a fixed volume of water per revolution. If the water supply can't keep up, the pump runs dry (cavitates), overheats, and wears out in months instead of years. Pump rebuilds run $150–$400. A $200 buffer tank pays for itself in the first season.
There's a second reason: many commercial jobs don't have a water hookup within hose reach. A buffer tank on your trailer means you bring your own water supply and don't depend on the customer's water at all.
Sizing Your Buffer Tank
| Setup | Washer GPM | Recommended Tank | Run Time (independent) |
|---|---|---|---|
| Homeowner / side hustle (hose bib supplemental) | 2–4 GPM | 50–100 gal | 12–50 min without any refill |
| Solo contractor (hose bib fed buffer) | 4–6 GPM | 100 gal | Buffer for low-flow; not full-day standalone |
| Solo contractor (fully independent) | 4–6 GPM | 200–300 gal | 6–8 hours of intermittent use |
| Commercial rig (fully independent) | 6–8 GPM | 500 gal | Full day; refill at end of day |
| Soft wash system (high volume, low pressure) | 10–20 GPM | 500+ gal | Depends on application volume |
How to Set Up a Gravity-Feed Buffer System
A gravity-feed setup is the simplest and most reliable plumbing for a buffer tank. The tank sits above the pressure washer's inlet, and gravity does the work.
What You Need
- Horizontal transport tank or vertical poly tank (elevated on truck bed or trailer)
- 1.5"–2" ball valve at the tank's bottom outlet
- 1.5"–2" clear braided suction hose, 3–6 feet to the washer inlet
- Inline strainer (Y-strainer) before the pump inlet to catch debris
- Garden hose quick-connect or camlock fitting at the pump inlet for fast setup
The Setup
Mount the tank so the outlet is at least 12"–18" above the pump inlet for positive head pressure. Connect the ball valve → strainer → suction hose → pump inlet. Keep the suction line as short and straight as possible — every foot of lift and every elbow reduces flow. Open the ball valve and your washer now has a gravity-fed water supply that won't starve the pump.
Pressure Washing Tank Guides
Tank Types That Work for Pressure Washing
Horizontal Transport Tanks (Best for Trailers)
Norwesco and Snyder horizontal transport tanks are the standard for pressure washing trailer rigs. They're low-profile (safe center of gravity), have a flat bottom for trailer mounting, and come with a bottom outlet and top fill. The 165-gallon and 305-gallon sizes are popular for mid-size contractor rigs that still want trailer portability.
Vertical Poly Tanks (Best for Truck Beds)
A 100 or 200-gallon vertical tank in a truck bed gives you a raised mounting position (good for gravity feed) and a small footprint. Flat-bottom vertical tanks with a low-center-of-gravity profile work best. Tanks taller than 36" can make a full pickup unstable when the load sloshes.
Rectangular Leg Tanks (Best for Custom Rigs)
Rectangular poly leg tanks (sometimes called "nurse tanks") fit snugly against truck bed walls and maximize space efficiency. They're harder to find than round tanks and typically cost more, but the space utilization on a commercial rig can be worth it.
Soft Wash Systems
Soft wash systems use high volume at low pressure (typically 60–200 PSI) to apply chemical treatments rather than water pressure for cleaning. They require substantially more water volume per hour than a standard pressure washer. A 500-gallon tank is the minimum practical size for a soft wash rig, and many operators run 500 + 500 in parallel (manifolded) for a full day's supply without refilling.
See our best soft wash system guide for specific equipment recommendations.
Frequently Asked Questions
No — if the tank is mounted higher than the pressure washer's inlet, gravity does the work. Your pressure washer's built-in pump pulls water directly from the tank through a suction line. You only need an additional pump if the tank is at the same level or below the washer, or if you're running long distances between tank and washer.
Most contractors use the customer's outdoor hose bib to refill between jobs or during breaks. A standard garden hose fills a 100-gallon tank in about 20–30 minutes at typical residential water pressure. Some contractors carry a fill pump and connect to fire hydrants (requires a permit and hydrant meter from the municipality) for faster refilling on large commercial jobs.