I am not sure about this thing.It is in between the impeller and the mulitport. I want to replace it. I think its corroding and causing metals in the pool...hence my recent issues with brown stains. Any ideas? Just replace with a piece of SCH40

Its like this but larger of course

That looks like a check valve. There aren't all that many other things it could be.

You might need a check valve in that location, depending on how your plumbing is setup, though that really isn't a very common location for a check valve. Could you describe the rest of your system? Do you have a spa, solar heat, fountain, etc?

No accessories. skimmer/main drain valve then pump basket just standard pump and impeller vertical PVC to lateral with brass check valve then filter

I'd remove it and see how the system performs. If you have an issue, you could always add a PVC check valve in it's place.