Buffer Tank / Float Tank for Pressure Washing — What It Is and Why You Need One

By Jason Geiman, King of Pressure Wash | 187,000+ views on YouTube

If you’re running a pressure washing rig without a buffer tank, you’re putting your pump at risk every single time you pull up to a job. A buffer tank — also called a float tank — is one of the most important components on any professional pressure washing setup, and it’s one that a lot of new operators overlook until they’ve already damaged their equipment.

I’ve been building and running pressure washing rigs for over 15 years, and I’ve seen firsthand what happens when operators try to run without a buffer tank or set one up incorrectly. In this post, I’ll explain exactly what a buffer tank does, why it matters, and how to set yours up properly so your pump stays protected on every job.

What Is a Buffer Tank?

A buffer tank is a water storage tank that sits between the water source (usually a garden spigot at the customer’s property) and your pressure washer pump. The tank fills with water from the spigot, and the pump draws from the tank instead of pulling directly from the spigot.

The tank has a float valve inside it — similar to the float valve in a toilet tank. When the water level drops as the pump draws water, the float valve opens and lets water flow in from the spigot. When the tank is full, the float valve closes. This creates a constant, reliable water supply for your pump regardless of what the spigot’s flow rate is.

Why You Need a Buffer Tank

Protects your pump from cavitation — This is the number one reason. Cavitation happens when your pump doesn’t get enough water and starts pulling air instead. When that happens, the pump creates tiny air bubbles that collapse violently inside the pump head, damaging the valves, pistons, and seals. Cavitation can destroy a pump in a matter of hours. A buffer tank ensures the pump always has a full, gravity-fed supply of water available.

Compensates for low-flow spigots — Not every property has a spigot that puts out enough water to feed your pump directly. Older homes, houses with long runs of pipe, or properties with low water pressure can all deliver less water than your pump needs. A buffer tank collects water from a slow spigot and stores it so the pump has enough supply to operate at full capacity.

Eliminates air in the line — When you connect a garden hose directly to your pump, air pockets in the hose can get pulled into the pump and cause sputtering, uneven pressure, and wear. The buffer tank gives air a chance to escape before the water reaches the pump.

Allows you to add chemical to your water supply — Some operators use the buffer tank to premix a mild solution or to add a pump lubricant to their water supply. This is an added benefit, not the primary purpose, but it’s useful on certain jobs.

How to Set Up a Buffer Tank Properly

Choosing the right tank size

For most professional pressure washing rigs running a 4-8 GPM machine, a 35 to 65 gallon buffer tank works well. The idea isn’t to carry hundreds of gallons of water to the job — it’s to have enough reserve that the pump never starves, even if the spigot’s flow rate dips. A 35-gallon tank gives you several minutes of buffer time, which is more than enough for the float valve to keep up.

Installing the float valve

The float valve mounts inside the tank, usually through a bulkhead fitting on the side. The garden hose from the customer’s spigot connects to the inlet side of the float valve. As the pump draws water and the level drops, the float opens and lets water in. When the tank is full, the float shuts the water off. Make sure the float valve you use can handle the flow rate you need — a cheap float valve that only passes 3 GPM won’t keep up with a pump pulling 5.5 GPM during sustained use.

Plumbing the outlet to the pump

The outlet from the buffer tank to the pump inlet should be at the bottom of the tank so it gravity feeds. Use a bulkhead fitting with a ball valve so you can shut it off when needed. The line from the tank to the pump should be at least the same diameter as the pump’s inlet — don’t restrict flow by using a smaller hose or fitting. A lot of guys use a 1” or 1.25” line from the tank to the pump to make sure there’s no restriction.

Mounting the tank on your rig

Mount the buffer tank higher than the pump inlet whenever possible. This gives you gravity feed, which means the pump doesn’t have to work as hard to pull water. Even a few inches of height difference helps. Secure the tank with straps or brackets — a full 50-gallon tank weighs over 400 pounds and will shift during transport if it’s not properly tied down.

Common Buffer Tank Mistakes

Running without one entirely. Some operators think they can just connect the garden hose directly to the pump and be fine. It might work on some properties with strong water pressure, but the first time you hit a house with a weak spigot, you’re going to starve your pump and risk serious damage. It’s not worth the gamble.

Using a tank that’s too small. A 5-gallon bucket with a float valve is not a proper buffer tank. You need enough volume to give the float valve time to react and keep up. A tank that’s too small will run dry the moment the spigot flow dips.

Restricting the outlet line. If you plumb a 3/4” garden hose from the tank to the pump inlet, you’re creating a bottleneck. The outlet line should be at least as large as the pump inlet, and bigger is better. Don’t undo the benefit of the buffer tank by choking the flow between the tank and the pump.

Not securing the tank for transport. A full buffer tank is heavy. If it shifts while you’re driving, it can damage your rig, your truck, or the plumbing connections. Strap it down properly.

Ignoring the float valve condition. Float valves wear out. The rubber seat can deteriorate, the float can crack, or the valve can stick. If your float valve isn’t working properly, water will either overflow or the tank will run dry. Check it regularly and replace it when it starts acting up.

Buffer Tank vs. Direct Feed — When Can You Skip It?

Some operators ask if they can skip the buffer tank on certain jobs. The honest answer is that there are situations where a direct feed works — but it’s always a risk. If the property has excellent water pressure and flow, and your pump isn’t pulling more GPM than the spigot can deliver, you might get away with a direct feed. But you won’t know the flow rate until you’re on site, and it can vary from house to house.

The buffer tank is cheap insurance. A decent tank, float valve, and fittings might cost you $100-$200 total. A new pump costs $500-$2,000 depending on your setup. The math is pretty simple. Run a buffer tank on every job and never worry about it.

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