What should be used on a sounding tape when assessing a water tank?

Using chalk on a sounding tape when assessing a water tank is appropriate because chalk allows for clear markings on the tape that represent the water level accurately. When the tape is immersed in the water, the chalk will show how high the water has risen, enabling a precise measurement of the tank's contents. This technique is particularly useful because it provides a visible reference point that can be easily read and understood.

In contrast, the other options do not provide the same level of clarity or utility. Water indicating paste is designed to identify the presence of moisture but would not mark the tape effectively for various water levels. Oil residue could interfere with the measurements and is not a reliable indicator of the water level in the tank. Paint may not adhere properly to the tape or could smudge, making it difficult to ascertain precise measurements. Therefore, chalk remains the best choice for clear and effective assessment.