I don't think snakes urinate, or atleast not in the same way mammals do (if they did, they'd drink alot more, and they'd have a faster metabolism). The white urates you see in the poo are the snake's equivalent of urine.
Easy way to measure length is to use a piece of string, just cut it or put a knot when the length is right. Weighing I use a digital scale (expensive lil things), and put a plastic box on it and tare it, and then add the snake.
For those who worry about snake pooping, why not use paper towel substrate? Hard to miss when they poop on that.
-13mur 6