I'm just starting on a 20x40 concrete block and liner pool and I don't know which return jets to use. How do yall do this? I've only had an above ground pool before and those jet "holders" had a flange on one side and a nut on the other and basically sandwich the pool wall in between them then the eyeball part screws in. Is this what I need to do on the block or is there something different I need? The old ones from the above ground pool don't have enough thread to sandwich it like that. How do I keep the jet firmly in place?