Check out your local "big box" Home Improvement Center. Go to the PVC pipe department and start checking for sizes. You will find a wide range of sizes in the "pipe connector / union" area. PVC connectors are strong enough for many "one time" jobs.

One time I made a sample model out of PVC for a special use race engine breather tank. I took it to Moon Equipment for fabrication and they had a good laugh, but they built it exactly like my sample. They now offer the same tank "as a production" breather tank.