Manway, manhole, thief hatch, gauge hatch, cleanout. Tank people use these words every day, and buyers often mix them up when they order parts. This page explains manway vs manhole, how both differ from a thief hatch and a cleanout, and which part to order for each job.
Manway vs manhole
On a storage tank, a manway and a manhole are the same thing: a bolted opening large enough for a person to climb through to inspect, clean or repair the tank. It is made up of a neck welded into the tank, a flange, a gasket and a cover.
- “Manhole” is the word API 650 and many older specs use (shell manhole, roof manhole).
- “Manway” is the word most fabricators, oilfield crews and parts suppliers use.
- Outside tank work, “manhole” usually means a street or sewer access with a cast-iron lid, which is a different product.
When you search for tank parts, both words lead to the same product. SteelFront sells a configurable round storage tank manway from 16″ to 36″, a matching bolted manway cover and a manway gasket.
Manway vs thief hatch
A thief hatch (also called a gauge hatch) is a small hatch, usually 8″, on the roof of a low-pressure production tank. Operators open it to measure the liquid level and pull samples. “Thieving” is the old oilfield term for sampling. Spring-loaded thief hatches also act as a pressure and vacuum vent.
| Manway | Thief hatch | Cleanout | |
|---|---|---|---|
| Purpose | Personnel and equipment entry for inspection, cleaning, repair | Gauging, sampling, pressure/vacuum relief | Removing settled solids at the tank floor |
| Location | Shell (side) or roof | Roof | Bottom of the shell |
| Typical size | 16″-36″ round | 8″ round | 24″ x 36″ rectangular |
| Opened | During shutdowns and inspections | Routinely, often daily | During cleanouts |
| Closure | Bolted cover and gasket | Hinged, latched lid, often spring-loaded | Bolted cover and gasket |
| SteelFront part | Round manway | Not sold | Cleanout frame and cover |
Manway vs cleanout
A manway is for getting in. A cleanout is for getting material out. A cleanout is a low, wide rectangular opening set at the bottom of the shell, so sand, sludge and paraffin can be shoveled or washed out. Many production and produced-water tanks have both: a 24″ shell or roof manway and a 24″ x 36″ cleanout. SteelFront’s cleanout frame is robot-welded from 2″ x 3″ x 1/4″ angle. It takes a 28″ x 40″ tank cleanout cover sealed with neoprene gasket.
Other access terms you will hear
- Davit manway: a manway whose cover hangs from a swing arm (davit), so one person can open a heavy cover safely.
- Hinged manway: the cover swings on a hinge instead of lifting off.
- Roof hatch or access hatch: a larger hinged hatch on a tank roof, often used with a platform.
- Nozzle: a smaller flanged or threaded connection for piping, not for access. See our half couplings and full couplings.
SteelFront sells bolted manways with separate covers. For hinged or davit manways, contact Wifco Steel Products, our parent company and manufacturer, about a custom request.
Safety note
Entering a tank through a manway is permit-required confined-space entry under OSHA 29 CFR 1910.146. Before opening any hatch or manway, isolate the tank, test the atmosphere and follow your company’s procedures. Opening a thief hatch on a production tank can expose workers to hydrocarbon vapors.
Ready to choose a size? Read the tank manway sizes guide or shop all tank manways.
Sources: API Standard 650; Kimray, “How Thief Hatches and Gauge Hatches Protect Oil Storage Tanks”; Emerson Enardo thief hatch documentation (8″ API bolt pattern); OSHA 29 CFR 1910.146.
Frequently asked questions
What is the difference between a manway and a manhole?
On a storage tank there is no real difference. Both are bolted openings large enough for a person to enter. “Manhole” is the term in API 650 and older specifications. “Manway” is the more common term in the tank and parts trade. In civil work, “manhole” usually means a buried sewer or utility access with a cast-iron lid.
What is a thief hatch on a tank?
A thief hatch is a small hatch on the roof of a low-pressure production tank, used to gauge the level and take (“thieve”) samples. Most are 8″ with an API 12 bolt pattern. Spring-loaded thief hatches also relieve tank pressure and vacuum at set points. A thief hatch is not a personnel entry point.
Can you enter a tank through a thief hatch?
No. A typical thief hatch is about 8 inches across, too small for a person. Tank entry is made through a manway, under a confined-space entry permit.
What is a manway at a gas station?
At a fuel station, the manway is the access cover over the top of an underground storage tank. It gives access to the submersible pump, fill and monitoring equipment. Those are UST components and are different from the bolted steel manways on aboveground tanks.
Why are manways round?
A round cover cannot fall through its own opening. A round flange also spreads bolt load evenly around the gasket, which helps it seal. Rectangular openings are used for cleanouts at the bottom of a tank, where a low, wide opening makes it easier to remove solids.