Trigonometric Phase Lines

Hi,

As part of a recent assignment I have been asked to draw a phase line for the function $\displaystyle \frac{dy}{dt} = sin(y)$. I can find the main equilibrium point easily ($\displaystyle y = 0$) but the problem I have is that $\displaystyle y = 180, y = 360, y = 540$ are also solutions. So in a way I have a phase line that continues infinitely. Is there any formal way of setting this out. The main idea that comes to mind is including an algebraic multiplier of both 180 and -180 on the phase line the stating $\displaystyle a \in Z$ when $\displaystyle a$ is the multiplier.

Thoughts?