Now I have two pipes, one is of 4'' diameter, the other one being 1 1/16'' in diameter and I need a pvc adapter to connect them. But I could not find anything like this online, so I need some help in this. Thank you.

now I have two pipes, one is of 4'' diameter, the other one being 1 1/16'' in diameter and i need a pvc adapter to connect them. but i could not find anything like this online, so i need some help in this. thank you.

Hey Toby, This is your lucky day. I'm going to give you some options.
You can reduce by bushing it down or a reducing coupling.
To bush down you will need a 4" PVC coupling and a 4 X 2" PVC Bushing, (see image) from Aubuchon Hardware model# 70242 at $8.49 a copy. Check it out at Find PVC Bushings and other Pipe Fittings PVC & CPVC at Aubuchon Hardware (http://plumbing.hardwarestore.com/52-333-pvc-bushings.aspx?viewAll=yes&sortBy=)

To reduce down you will need a 4 X 2" PVC reducing coupling, (see image) #70142 from Genova Products at $8.29. Go see at; Reducing Coupling, 4" x 2" # 70142 by Genova Products (http://plumbing.hardwarestore.com/52-333-pvc-unions-and-couplings/reducing-coupling-305805.aspx)
You can pick up a 2 X 1" PVC bushing almost anyplace so you're all set to go.
Don't forget to purchase purple primer and PVC cement. Good luck, Tom

Good advice, Tom. I just want to add: all you need can be purchased for few pennies in Home Depot.