Skimmer (NAC 6) issue

[Midway]

I am having this issue with this skimmer. I have it in my sump, works great, skims the heck out of the water. I turn it off to feed my corals, when i turn it back on, it does not do anything, there is no bubbles nothing. I have to take it out of the sump, drain all the water out of it, i sink it again and sometimes it starts to skim again sometimes i have to do it a couple of times to start it again. Something i'm doing wrong or what? It suppose to start right away when i turn it on.

If you have one of them, did you have the same issue i'm having?

Let me know how can i resolve this please.

Thanks,

Manny