Newbie looking for plumbing assistance

[Trevor W]

Maybe I misunderstood your post but I would use the flexible hose on the return line and the pvc for the drains. And use a gate valve for the main drain not a ball valve. As far as the 90 from your bulkhead depends if your bulkhead is slip or thread either way your just need a 90 elbow with threads or if its slip just a piece of pvc to go between the bulkhead and elbow. Im assuming that your drains are coming from the back of the tank and not from the bottom or an external overflow?