Tank processing is also referred to as "deep tank" processing or "dip and dunk" processing. The equipment requirements are greater than for tray processing; a tank for each processing solution is required, along with film hangers for each sheet of film the photographer wishes to process. A film hanger is a metal frame with perforated edges which holds a single sheet or multiple sheets (usually four) of film. The films are inserted into the film hangers, and then submerged into the tank. Agitation is performed by lifting the hangers out of the tank, tilting them to one side to allow them to drain for a brief moment, resubmerging them, lifting and tilting to the other side, and resubmerging. Many photographers will bang or tap the hangers on the tank's top after the second tilt, to dislodge any air bubbles that have stuck to the film.
Tanks are also helpful for long development techniques such as "stand" development. Stand development is very individualized, and every practitioner has his or her own routine, but in general, after an initial agitation in the developer, film is simply allowed to stand motionless in (generally highly dilute) developer, with no agitation, for very long intervals, up to hours.
Large tank processing has higher equipment requirements, and a larger volume of solution is required for each step. A tank for 4×5 inch film can require 2 litres (64 ounces) of chemistry, and most tanks for 8×10 inch film require from 4 litres (1 gallon) to 13 l (3.5 gallons). Many large tanks come with floating lids to reduce possible oxidation of solution. Also, despite such large chemical volumes, some tanks do not allow very many films to be processed at a single time; generally six to ten or so. However, film hangers that hold four sheets of film when used in larger tanks can process many sheets of film at the same time. Tank processing, like using trays, must also be performed in the dark. Some photographers report uneven development using this method.
There are also daylight tanks accepting sheet film, usually adjustable to multiple existing sheet formats - e. g. inch and metric, and allowing the processing the sheet film in daylight. They have to be loaded in the dark, though. The stainless steel Nikor tank accepts up to 12 sheets of film, 4x5" size maximum, and requires about 1 liter of chemistry. These tanks have long been discontinued, and are only available used. Some people report uneven development and emulsion scratching with this device (a result of steel "spider" presence, separating the sheets in tank's "cage" ), but many users get excellent results with it - the right loading and infrequent agitation are perhaps the keys to success. The current make plastic Combi-Plan tank accepts up to 6 sheets of film, and works nicely, though the overall quality of manufacture is not too high, and the tank has a number of small plastic details, easy to break or lose. But this tank is also quite capable of excellent performance.