Welcome to JustAnswer. Normally there is no sugar in the urine because excess glucose is removed by the kidneys. When the sugar is so very high that it overwhelms the kidneys, then sugar spills into the urine. The way to eliminate sugar in the urine is to control blood glucose. That means careful meal planning (both as to content and amount), and oral medications or proper insulin dosage.
Drinking water will dilute the sugar content. However, you are having the test done to see if your blood glucose control is good, or if your diabetes treatment needs altering. Deliberately undermining the reliability of the test does you a great disservice. It is better to know that the sugar is there so that your treatment can be altered to accommodate it rather than overloading yourself with water and making the test itself worthless while your diabetes goes along out of control.