Do large aircraft accumulate water in their tanks?
If so, how is it drained? How often is it drained? At what rate per hour does it accumulate? If not what was done to circumvent the problem?
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AFAIK all aircrafts accumulate water in their tanks. Since you ask for large aircraft acccording to wikipeadia:
FAA definition of large aircraft
The US Federal Aviation Administration defines a large aircraft as any aircraft with a certificated maximum takeoff weight of more than 12,500 lb (5,700 kg)
EASA definition of large aircraft
The European Aviation Safety Agency (EASA) defines a large aircraft as either "an aeroplane with a maximum take-off mass of more than 5,700 kilograms (12,600 pounds) or a multi-engined helicopter."
Here is Airbus A340 draining process with explanations on youtube
Here you can find EASA regulations about draining https://www.easa.europa.eu/download/etso/ETSO-C76b_CS-ETSO_11.pdf
Here is FAA regulations about water draining https://www.faa.gov/documentLibrary/media/Advisory_Circular/AC20-125.pdf
On FAA AC 20-125 p.7 states
WATER REMOVAL/PREVENTION. Water is best removed from jet fuel by passing the through approved filtration/separation equipment. A two-hour settling period and the use of floating suction to drain fuel from the top of a storage tank are also recommended to help prevent water from being introduced into a fuel system. Water will readily settle-out of aviation gasoline; therefore, filters/separators are not required for water removal, however, they are necessary for removal of solids. The best means to minimize the amount of water entering a fuel system is the inspection and proper maintenance of equipment and the training of ground and flight personnel.
Also FAA AC 20-125, Water In Aviation Fuels, para 7 c suggests that it may be necessary to gently rock the wings of some aircraft while draining the sump in order to completely drain all the water.