Size of fittings for Thien separator

Based upon reading various posts and articles it is my understanding that the inlet and outlet fittings for a Thien separator (built into a metal garbage can) should be the same size as the inlet fitting on the dust collector.

My Harbor Freight dust collector uses a 4 7/8s inch inlet. I would assume that this is considered to be a 5”.

Now to my questions:
1. Am I correct in wanting to use a 5” elbow and a 5” straight fittings on the thien?
2. I am having a problem finding 5” pvc fittings. I don’t really want to pay around $30 each for metal ones. Do you know of a cheap source for the fittings?

-- Jesse, Saint Louis, Missouri