Key takeaways
- Plan every stop from the last verified pump volume; treat nameplate trap size only as a ceiling.
- A full pump-out removes the trap's entire liquid contents, so a stop's volume stays roughly constant no matter how overdue it is.
- Stops-until-full is division with a haircut: usable tank gallons ÷ expected gallons per stop, minus a buffer for wash water and residual load.
- Nameplate sizes are category labels; actual liquid capacity and grease-storage volume are different numbers.
- Legal payload is a second ceiling: a truck can be weight-full while the tank still shows room.
- Unknown-size stops get a conservative planning number, an early slot in the route, and a measurement on the first visit.
- Recording actual gallons at every stop is what makes next month's plan honest.
Grease traps run from small indoor units to in-ground interceptors holding several thousand gallons, but the size on a customer record is a ceiling, not a planning number. Plan each stop from the gallons you last pumped there, fall back to nameplate capacity when you must, and set stops-until-full per truck by dividing usable tank gallons by expected stop gallons. That is the load math underneath planning grease trap pumping routes and how many traps a truck can serve in a day, and it is the backbone of DynoRoute's capacity-based routing for grease trap fleets.
Nearly everything published about trap sizing is written for the restaurant buying one. You sit on the other side of the hose: you already know your tank sizes, and the question that matters is whether truck 2 can take one more 1,500-gallon vault before its disposal run. Even cleaning frequency, a compliance lever on the customer's side, barely changes what a full pump-out puts in your tank. Size math for the truck deserves its own article.
I build route planning software for vacuum truck fleets, and I have spent this year interviewing the people who dispatch them. This article writes down the math the best of them carry in their heads.
How many gallons should dispatch put against each stop?
Use the last verified pump volume for that exact stop. If you do not have one, use the average of the last few pulls; failing that, treat nameplate liquid capacity as an upper bound; and if the size is unknown, book the stop conservatively until a first service proves it out.
The hierarchy works because a grease trap does not fill the way a fuel tank does. It is a flow-through device that sits full of liquid all the time. What changes between services is how much of that liquid is grease and settled solids, not how many gallons are inside. On a full evacuation the truck takes all of it, grease mat and water column included, which is why the same stop tends to give up close to the same gallons every visit. Last quarter's ticket beats any sizing chart.
Written as a fallback list for the office:
- Last verified pump volume for this stop. Use it.
- Average of recent pulls, when the latest ticket looks off (partial service, split load, a different truck's gauge).
- Nameplate capacity, treated strictly as a ceiling.
- A conservative default for stops nobody has sized, covered below.
Nameplate sits third for two reasons. Actual liquid capacity differs from the label, as the next section shows. And the label in your records may describe a trap that was swapped, re-plumbed, or typed from memory years ago. A number your own gauge produced beats a number someone once wrote on an intake form.
What common trap sizes and capacities mean on the truck
Indoor hydromechanical traps are rated by flow, in gallons per minute; outdoor gravity interceptors are quoted by nominal liquid capacity, starting around 500 gallons and running past 5,000. Neither figure is exactly what your truck takes on. Nominal size, actual liquid capacity, and grease storage are three different numbers.
Hydromechanical traps are the smaller units in or near the kitchen, certified by flow rate rather than volume. For load planning they are small pulls, booked in the tens of gallons, and one address often holds more than one. A kitchen with two indoor traps and an outdoor vault is one stop and three pulls, which is its own planning problem — servicing multi-trap locations covers it.
Gravity interceptors are the in-ground vaults, quoted by capacity, and Phoenix's sizing table starts them at a 500-gallon minimum. Above that, the familiar labels (750, 1,000, 1,500) are categories rather than measurements: Xerxes lists actual liquid capacities of 515, 755, 1,001, 1,254, and 1,500 gallons for its common nominal models, continuing through 2,100, 2,622, 3,144, 4,188, and 5,312 gallons at the large end.
One split inside those numbers matters more than it looks. On the 1,001-gallon model, Xerxes allocates 590 gallons to grease storage and 308 gallons to solids storage. A "1,000-gallon" interceptor is 1,000 gallons of total liquid, not 1,000 gallons of recoverable grease. For your plan the total is what counts, since a full pump-out takes the water along with the grease. It is also why a customer describing "1,000 gallons of grease" is describing a device that does not exist.
How many stops fit before the truck has to unload?
To find how many stops fit before a disposal run, divide the truck's usable tank gallons by expected gallons per stop and round down. A 2,000-gallon tank holds two 1,000-gallon pulls or forty 50-gallon indoor traps; a 4,000-gallon tank doubles both. Those are ceilings, not schedules.
A boundary line before the arithmetic: every number in this section is an illustrative ceiling built on stated assumptions. The truck starts empty, every trap is fully evacuated, and nothing else rides in the tank. Real days break all three assumptions.
Grease trucks commonly carry tanks between 1,500 and 5,000 gallons (KeeVac's grease collection packages span roughly that range), so read the column nearest your own trucks:
| Expected pull per stop | 2,000-gal tank | 2,500-gal tank | 4,000-gal tank |
|---|---|---|---|
| 50 gal (indoor trap) | 40 stops | 50 stops | 80 stops |
| 500 gal | 4 | 5 | 8 |
| 1,000 gal | 2 | 2 | 4 |
| 1,500 gal | 1 | 1 | 2 |
Illustrative ceilings: usable tank gallons ÷ expected pull per stop, rounded down.
The table says two useful things. On small-trap routes, the tank is never the constraint; nobody runs forty indoor traps in a day, so drive time and service time bind long before volume does. On interceptor routes the tank is nearly the only constraint: a 2,500-gallon truck is done after two 1,000-gallon vaults and change, and the real routing decision becomes where the disposal return sits in the route.
Mixed routes are where the division stops being obvious. Say one of your trucks runs a 2,500-gallon tank, and tomorrow's sheet holds one 1,000-gallon interceptor, two 500s, and five indoor traps booked at 50 gallons each. That totals 2,250 gallons, so it fits with 250 to spare. Whether that 250 is a cushion or a coin flip is what separates capacity math from capacity-honest math.
Why the truck fills sooner than the math says
The truck fills sooner than the division says because the tank rarely starts empty and every stop brings aboard more than the trap's rated gallons. Residual load, wash-down water, stale size records, and legal payload each shave the margin, and they stack.
Run that 2,250-gallon route honestly, with illustrative numbers. The truck came home with a wet hose and a partial load, so say 100 gallons are already aboard at the 6 a.m. start. Every full service adds wash-down water, because the crew rinses trap walls and pushes solids toward the suction line; call it 25 gallons a stop across eight stops, another 200 — your crews will have their own number. The 250-gallon cushion is gone before a single trap runs bigger than its record.
And records err bigger. The nominal-versus-actual gap at the model level is trivial; a nominal 1,000 measuring 1,001 gallons will not hurt you. Records rot at the site level: interceptors get replaced, sizes get typed from memory, and a vault nobody has opened in years can pump at nothing like its listed figure. A route plan built on nameplate numbers inherits every one of those errors at once.
Weight is the ceiling most load spreadsheets skip. Tank volume and legal payload are separate limits — FlowMark's truck sizing guide pairs a roughly 33,000-lb GVWR chassis with about a 2,500-gallon tank — and where your trucks land depends on the chassis, the axles, and what else is mounted on them. A truck can be weight-full while the sight glass still shows room. Plan to whichever ceiling arrives first.
The practical fix is a standing buffer. Pick a hold-back, say 10 percent of usable capacity, applied the same way on every truck, and plan routes to the buffered number. The division stays the same — it just runs on honest gallons.
Planning a stop with an unknown or disputed size
Book an unsized stop conservatively, run it early in the route, and turn the first service into a measurement visit. An unknown vault booked as a small pull is how a truck ends up full two stops before the end of the sheet.
Workable defaults until you know better: book an unconfirmed outdoor interceptor at 1,000 gallons, mid-range for the common sizes above, and an unconfirmed indoor trap at 50. When paperwork and site photos disagree, plan from the larger figure. These are planning conventions rather than statistics; set them to what your service area actually installs, then apply them everywhere.
Position matters as much as the number. An oversized surprise at stop two leaves options: pull the disposal return earlier, or shift a later stop to another truck. The same surprise at the second-to-last stop leaves a full truck and an unserviced customer. Unknowns go early.
Then make the first visit pay. The driver records what the office could not know — gallons pulled off the truck's gauge, compartments and lids, photos of the trap and its access, anything that made the stop slow — and the office writes it to the record the same day. When a customer swears the trap is a 500 and it pulls 900 twice running, the gauge wins the dispute. Since disposal costs track gallons, the gauge should settle the billing conversation too.
How actual gallons make the next route honest
The most valuable number your trucks produce is the actual gallons pumped at each stop. Written back to the customer record, it replaces nameplate guesswork with arithmetic on real pulls, and it is the one input that improves every time you service.
The loop is short: driver records the pull, office writes it to the stop, next plan uses it. Once it runs, most of this article collapses into rule one of the fallback hierarchy — real numbers everywhere, defaults only for first visits. The loop usually breaks in the middle. Gallons live on paper tickets, get typed in on Friday, and never reach the plan.
That loop is what DynoRoute is built around, and every mechanism in this article maps to something the software actually holds. Each stop carries its expected volume as a capacity field, kept honest because the gallons your driver logs at the trap — with timestamped, geotagged photo proof — write back to the stop for the next cycle. Each truck carries a fill limit, so recurring routes are planned against the buffered number instead of nameplate hope, with disposal returns placed in the route rather than improvised mid-day. When a stop runs bigger than its record, the AI dispatcher re-matches the rest of the day across your trucks with the same capacity math. And because disposal costs track gallons, the logged pull flows into QuickBooks for the invoice — the gauge settles billing, not just routing. The rest of what grease trap software should do for a pumping fleet is on the hub page.
If you would rather your load plans came from real pulls than from nameplate sizes, get started with DynoRoute — a CSV of your customer list and the last pump volumes you trust is enough to plan the first day against your trucks' real fill limits.
