What diameter pipes should I use for a 90 gallon tank ? Thanks !

I am working on a 90 gallon project and I need to get some plumbing done. I have a 30 gallon tank that I am going to use for a refugium. I have never done a sump befor so I don't want to screw it up. I was going to us pvc to run the plumbing so I need to get a idea on what size to get and also...