Ultrasonic tanks have electronic transducers fitted to the base or the sides of the main tank. High frequencies are generated in the fluid by the transducers, and this causes thousands of micro bubbles to be generated. The bubbles are tiny, and as they move they tend to dislodge dirt and other particles, drawing them into the solution. They are generated in almost inaccessible places, thus making a highly effective cleaning machine.

These tanks are used in many trades, and it is common to see them in dental and optical labs as well as in the electronic and engineering fields.

Some units have heaters, but these are more common in engineering. Most clock fluids are best left reasonably cool, or their effective ingredients may evaporate.

Be wary of tanks that incorporate a drain tap. This sounds like a good idea, but in fact ultrasonics can damage welds over time, and sooner or later most drain taps leak at the join.

A wire basket, similar to a chip basket, can be used to immerse small parts. The nearer the transducers you put items, the better the cleaning effect, but you don't want to have to use your hands to pick things off the bottom. In fact most fluids are not suitable to contact with skin. If you wear gloves, be sure to select ones that are resistant to solvents.

To preserve the efficiency of the fluid, most repairers pre-soak dirty parts before putting them into the tank. A simple way to achieve this is to buy an old aluminium catering saucepan with a lid from a charity shop, and when the tank needs fresh fluid, put the old fluid into the saucepan. Immerse dirty movements in the used fluid, leaving them to soak if necessary. When much of the grime has loosened, shake off the surplus fluid and place the movement into the tank. Stubborn grease can be dislodged with a paintbrush, but use one with a wooden handle and pure bristles, or the solvents may dissolve it. This method of pre-soaking will help extend the life of the fluid considerably. If you have the space and do enough clocks pre day, you can extend this further by having a succession of fluids in increasing cleanliness. Just shift them all down one, each time you replace the fluid in the tank. Discard the oldest, but please don't throw it down the drain. Dispose of it thoughtfully. Two pre-cleaning containers are normally adequate.

Fluids are not particularly expensive in their own right, but the legislation surrounding storage, handling and distribution of flammable and hazardous liquids has increased the cost to the end user. It pays to protect the fluid in the tank from contamination.

Cleaned items need to be rinsed. This will prevent verdigris forming by neutralising the cleaner, and good rinses also contain brass brighteners which can have a remarkable effect on mass-produced movements, making them look as they did when they left their factory.

There is no need to use the ultrasonic tank to rinse the items. Yet another saucepan filled with pre-rinsing fluid is all that you need. You can use the same principle of a pre-rinse by using old rinse before putting the parts into clean liquid. Rinse will become quickly contaminated by excess cleaner.

Always read the instructions that came with the tank and with the fluids. Take care when dealing with flammable liquids, and make sure you work in a well ventilated area.