Hello I am removing a tub and replacing it with a prefab shower base and need some drain and waste help. I have good access underneath. Existing is a 3" copper waste pipe and I was thinking that I could cut a small section out and install a 3x3x2 sanitary tee to pick up the shower and cap off the exisitng 1-1/2 which is further up line but wasn't sure how to go from copper to pvc thank you

You will have to use 3"Copper x 3"PVC dedicated Mission Fitting that fits your installation.

You will have to use 3"Copper x 3"PVC dedicated Mission Fitting that fits your installation.
Hi milo thanks for quick response where can I get a mission fitting and how does the copper side assemble?

It is a specialty coupling that can be purchased in professional plumbing supply houses, like Ferguson Enterprises. But I have also seen them in Home Depot and Lowe's.

If you have difficulties purchasing this specific coupling, you can also use 3"x3" Flex Seal coupling of given size. Home Depot carries them.