Allendale for me as recommended by Ted (and originally by Ash).
They do a range of products for different ultrasonic applications Johnny and worth a look.
I made a local jewellers eye water a few years ago when I told him I'd put my 20 year old Citizen watch in my ultrasonic cleaner because it was so gunked up (it was safe to 50mtrs according to the dial!). It came up like new and still works fine, it was one of the original eco drives👍. Citizen watches are like an old Honda, will go on forever if used daily🙂