English to Dutch Tech/Engineering Mechanics / Mech Engineering liquid measurement

This is, apparently, a device used in a flotation tank (which is constantly stirred and agitated) to create a small area of relative calm in the liquid where a float/ultrasonic monitor is placed to properly measure the level of the slurry in the tank. I have been able to find patents describing this in English, but no workable translation (at all) into Dutch.

Example sentence:
"The float is normally placed inside a stillwell and may be kept clean by a continuous spray water addition."