Peeing in a cup/FMU question

Totally a dumb question, but when you pee in a cup to test first thing in the morning. Do you only pee a little bit in the cup (like 1/4 or 1/2 of the cup then the rest in the toilet) or do you pee it all into the cup.

Basically am I peeing too much into the cup and maybe diluting my sample?