This information provided to me courtesy of "Keith."
To determine the weight of your urine, first weigh the container. Then put in several ounces of urine. Get an exact measurement, and weigh. Divide this by the number of ounces placed on the scale.
The weight varies, though not greatly, by the quantity of water you drink. I (Keith) drink lots because I had kidney stones several years ago and this is helps prevent them. You will be fairly close with the 1.16666 figure.