Astro Powerhead questions

Hey guys! I just got a new powerhead made by Astro, the AS-1000.
I've never used it before and I can't seem to find specific information on it... (forgot to ask the LFS owner)

Firstly, the powerhead comes with this T shaped pipe, with one end of the T connecting to the powerhead, the other end pumping water out, and the middle joint connects to a small clear bendy plastic tube. I assume it's for water to flow out... but when I connect it, nothing comes out from it. Only from the main output pipe. Does anyone have any idea what's it for??

secondly, do I need filter media? Though I can't seem to find anywhere to place it....

Thanks!! Appreciate your help