Watch movements require cleaning periodically as part of a service and professional watchmakers use specially designed machines to carry out the process relatively quickly and efficiently. It can be, and would traditionally have been done manually by hand using similar cleaning solutions and degreasers, small brushes and bits of peg wood sharpened to clean out pinion holes, but the cleaning solutions can be dangerous and it’s a very time consuming and laborious process to be done well.
Why do watch movements require cleaning? Mechanical watch movements require lubricating with oil to run as do the mechanical parts in analogue quartz watches (but quartz movements are usually replaced, or deemed beyond economical repair rather than serviced). Over time the oil will degrade, the quality of oils has greatly improved and there is now a wide array of not just high quality natural mineral oils but also fully synthetic oils, however the improvements have simply increased service intervals, the oil still degrades with time. The co-axial escapement was designed by George Daniels to run without lubrication as to further overcome the problem and increase service intervals (but I think Omega may lubricate it? let me know if you know).
This is the Elma Solvex VA which is one of the most advanced watchmakers watch cleaning machines
An average recommended clean and service interval is probably around every 3 years but it varies from one manufacturer to the next. The longer you leave it the more inaccurate time keeping will become and you increase the risk of possible damage.
To clean a watch movement effectively it has to be disassembled and for a number of other reasons, not least that some of the parts cannot be put through the process. Once disassembled the parts are placed in compartmented baskets or holders to prevent the parts colliding and damaging each other during the cleaning process.
Each cleaning machine is different but basically the baskets containing the parts are spun in a cleaning solution and then a series of rinsing solutions. There is more than one rinse, although it’s usually the same solution as the first becomes contaminated with dirt and solution from the clean, so there is a second and a third.
The most advanced machines automatically move the baskets containing the parts through the different solutions and have programmable timers, ultrasonic cleaning, and vacuum and fume extraction, whereas basic machines just provide motorised spinning action for the baskets but require you to manually move the basket from one solution to the next.
Here is a great video showing the use of a professional but basic machine