Welcome to saltwater hobby
It could become overwhelming sometimes don't let that discourage u.
While my bulk head is inch, does it mean the diameter of the PVC and flexible hose is also 1 inch?
Yes
U will have gate or ball valve on main drain pipe to control the flow .
No need to control flow on return line.
I do not understand why u need 90 degree elbow?
It would help if you could draw out on a paper what you are trying to achieve.
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