Pressure Washing Trailer & Rig Setup
A rig is three decisions — what carries it, how much water it holds, and how that water gets to the pump. Everything else is preference.
The one that gets guessed at is the tank. Most residential spigots deliver 4–6 GPM while a contractor machine draws 5.5–8, and the buffer tank exists to cover that shortfall for every minute the trigger is down. So the size is calculable: (machine GPM − spigot GPM) × minutes of trigger time. The calculator below works that back from the square footage of the job. Then: platform, plumbing, layout, and the weight numbers that decide your axle.
Buffer tank and water supply calculator
1 · The job
Typical for 20" surface cleaner — smooth concrete: 1,250–1,550 sq ft/hr on site, already allowing for overlap, turns, and trigger-off time.
2 · The flow
Don't assume the spigot. Time it: a 5-gallon bucket in 60 seconds is 5 GPM. Residential bibs commonly run 4–6 GPM and drop further through a long or narrow hose — measure it at the property, on the hose you actually use.
Buffer tank needed
54 gal
2,500 sq ft ÷ 1,400 sq ft/hr = 107.1 min of trigger time · 589 gal of water total
What that means for the rig
- Shortfall while the trigger is down
- 0.5 GPM
- Smallest stocked tank that covers it
- 65 gal
- Water weight when full (8.34 lb/gal)
- 542 lb
- That tank buys you
- 130 min of continuous trigger time
Size up from here, not down. This is the minimum for one continuous run — it assumes you start full and never wait. Most operators carry the next size up so the tank is a buffer rather than a countdown.
Every number here starts with the area. Guess it and you size the tank for a job you haven't actually measured — measure the property from satellite imagery before you load the trailer.
Production rates match the ranges in the surface cleaner guide. Time the spigot at the property rather than trusting a default — it is the input that moves this answer most.
Skid, Open Trailer, or Enclosed
This gets argued as a status question and it isn't one. It's a question about where you work: residential driveways in tight suburbs reward the thing you can park, and commercial routes reward the thing that carries water. Most operators start with a skid and move up when tank capacity — not ambition — becomes the constraint.
Truck-bed skid
Starting out, tight suburbs- Cheapest way to a working setup
- Parks anywhere the truck parks
- Comes inside at night — theft matters
- No second registration or storage
- Tank capacity capped by bed size and payload
- Truck bed is permanently occupied
- Loading and unloading is a job in itself
Open utility trailer
The common working answer- 5×10 holds a machine, two reels, and 100+ gal
- Truck bed stays free
- Can be dropped on site or at a shop
- Cheap to build and easy to modify
- Visible and easy to strip — everything is exposed
- Backing into residential driveways takes practice
- Needs somewhere to live between jobs
Enclosed trailer
Crews, commercial routes, wet climates- Gear is locked, dry, and out of sight
- Rolling billboard with your wrap on it
- Work out of it in weather
- Heaviest and most expensive option
- Ventilation is mandatory with a gas engine
- Worst option for tight residential access
The Tank Is a Flow Problem, Not a Volume One
The instinct is to ask how much water the job needs and buy a tank that size. That's the wrong question, and it's why so many rigs carry a quarter ton of water they never use.
With a float valve fitted, the spigot is feeding the tank the entire time you're working. So the tank never has to hold the job — it only has to hold the difference between what your machine draws and what the spigot delivers, for as long as the trigger stays down. A 5.5 GPM machine on a 4 GPM bib is 1.5 GPM short; over a 45-minute run that's 68 gallons, not the 248 the job actually consumed.
Which is also why the spigot is worth measuring rather than assuming. A bucket and a watch at the start of the job changes the answer more than any other input — and on a property with a slow bib, it's what tells you to bring water instead of finding out an hour in.
Trigger time comes from area and production rate, so the whole chain starts at the square footage. The surface cleaner guide covers where those production rates come from.
- Area
- 2,500 sq ft
- Production, 20" cleaner
- 1,400 sq ft/hr
- Trigger time
- 107 min
- Machine flow
- 5.5 GPM
- Water consumed
- 589 gal
- Spigot measured at
- 4 GPM
- Shortfall
- 1.5 GPM
- Buffer needed
- 161 gal
- Tank to buy
- 225 gal
- Water weight when full
- 1,877 lb
Note the last two lines. The tank that solves the water problem is also 1,877 lb of load — which is a trailer axle and tow-rating decision before it is a plumbing one.
Five Plumbing Rules That Save a Pump
Pumps rarely fail from use. They fail from starvation — running dry, running against a restriction, or cavitating on air. Every rule below exists to keep water arriving faster than the pump can ask for it.
- Never neck down into the pumpThe tank outlet and the line to the pump inlet should be at least as large as the inlet itself — 1 inch is common where the pump wants it. A 3/4-inch garden hose feeding a hungry pump is the single most common cause of cavitation on a home-built rig, and it sounds like a rattle before it becomes a rebuild.
- Let gravity do the feedingMount the tank so its outlet sits above the pump inlet. A pump that has to lift water is a pump working against itself, and the margin disappears the moment the tank runs low — which is exactly when you need it most.
- Float valve, alwaysA float valve fed by the property's hose refills the tank continuously while you work. This is what lets a 65-gallon tank support a 45-minute run: the tank isn't your total water, it's the buffer between what you draw and what the spigot delivers.
- Filter before the pump, not afterAn inline filter on the inlet side catches the grit that comes with well water and old municipal lines. Cheap to fit, cheap to clean, and it protects the most expensive component on the trailer.
- Plumb for winter on day oneA low-point drain and a way to run antifreeze through the pump take an hour to add during the build and are close to impossible to retrofit neatly. One hard freeze on an undrained pump ends the season early.
Layout, Weight, and the Things That Bite Later
A rig gets built once and used every day for years, so the decisions that feel minor during the build are the ones you pay for daily. Water at 8.34 lb per gallon is the constraint underneath most of them — compare your loaded total against the trailer's GVWR and your truck's tow rating, not against its empty weight.
Tongue weight is the whole ballgame
Roughly 10–15% of the loaded weight should sit on the tongue. Put the tank forward of the axle, not behind it — a trailer loaded tail-heavy sways at highway speed, and a tank is by far the heaviest thing you'll carry.
Reels where you can reach them
You'll pull hose dozens of times a day. Mounting reels at waist height on the curb side keeps you off the road and out of a daily fight with your own equipment.
Secure like it's going to stop suddenly
At highway speed an unsecured 250 lb machine becomes a projectile. Steel cages or 2-inch polyester straps rated well above the load — and check them, because vibration loosens everything eventually.
Ventilate anything enclosed
A gas engine in an enclosed trailer needs real airflow, not a vent you meant to add. This is a life-safety item and it belongs in the build, not the punch list.
Separate chemical from water
Soft wash chemical gets its own dedicated tank and its own lines. Sharing plumbing between your water supply and your sodium hypochlorite is how you find out what SH does to a pump seal.
Leave room to work
The commonest regret on a first build is packing the deck so tightly there's nowhere to stand. Leave a working aisle — you'll use it every day for the life of the rig.
Running a separate soft wash system off the same trailer? Chemical strengths, batch splits, and what a downstream injector can actually reach are in the soft wash mix calculator. What the rig costs relative to everything else you need to launch is broken down in pressure washing startup costs.
Rig Questions Operators Ask
Tank sizing, trailer size, plumbing, weight, and what it costs to build.
Size it from the shortfall, not from a rule of thumb. Subtract the property's spigot flow from your machine's GPM — that difference is what the tank has to cover for every minute the trigger is down. A 5.5 GPM machine on a 4 GPM spigot runs 1.5 GPM short, so a 45-minute continuous run needs about 68 gallons, which is why 65 and 100 gallon tanks are the common residential answers. Most operators then buy the next size up so the tank is a buffer rather than a countdown.
Two reasons. The first is flow: most residential spigots deliver 4–6 GPM, and a contractor machine at 5.5–8 GPM can outrun that, so the tank absorbs the shortfall. The second is pump protection, and it applies even when the spigot keeps up — feeding a pump directly off a hose bib means any pressure drop, kinked hose, or someone shutting a valve inside the house can starve it and cause cavitation damage. The tank breaks that connection, which is why rigs carry one regardless.
A 5×8 utility trailer fits a skid machine, one reel, and a modest tank, and maneuvers easily in residential driveways. A 5×10 is the common step up — roughly 50 square feet of deck, enough for the machine, two reels, and a 100-gallon tank while still towing behind a standard half-ton pickup. Go larger only when the work justifies it: every extra foot is harder to park on a suburban street, which is where most residential jobs actually happen.
Water weighs 8.34 pounds per gallon, so a 100-gallon tank is 834 pounds of water alone, and a 225-gallon tank is about 1,877 pounds before you bolt down anything else. This is the number that decides your trailer's axle rating and your truck's tow capacity, and it is the most commonly underestimated figure in a rig build. Add the machine, reels, hose, and surface cleaners on top, then compare the total against the trailer's GVWR — not its empty weight.
Three rules cover most failures. Keep the tank outlet at least as large as the pump inlet — plumbing a 3/4-inch garden hose into a pump that wants more is a bottleneck that starves it. Mount the tank higher than the pump inlet so it gravity-feeds rather than asking the pump to lift. And put a float valve in the tank fed by the property's hose so the spigot refills continuously while you work, which is what lets a small tank support a long run.
A skid in a truck bed or enclosed van is cheaper to start, easier to park, and disappears at night, which matters for theft. A trailer carries more water and gear, keeps the truck bed free, and can be dropped at a site — but it needs somewhere to live, is harder to back into a driveway, and is a visible target. Most solo operators start with a skid and move to a trailer when tank capacity, not ambition, becomes the constraint.
The trailer and tank are rarely the expensive part. A used 5×10 utility trailer, a 100-gallon tank, a float valve, hose reels, and plumbing typically land in the low thousands; the belt-drive machine and surface cleaner are usually the larger line. Budget for the unglamorous items that get forgotten — quick disconnects, hose, straps rated for the load, a tank cage, and wiring — because they are what turn a pile of equipment into a rig you can actually work out of.
Everything the Rig Has to Support
What it runs, what it applies, what it costs, and the jobs it has to cover.
Know the Job Before You Load the Trailer
Tank size, water, chemical, and hours all start from one number: how much surface there is. Measure any property from satellite imagery in under a minute. 1 free measurement, no credit card.