Just an idea...but you might try the pump-to-sump idea. But buy a cheap rubbermaid (or similar) container and mount above the main tank. You can more easily cut a whole in the non-glass refugium/sump an install a bulkhead fitting at an elevated height in the refugium/sump to act as a gravity fed overflow back to the main tank....that won't have the possibility of draining entirely if the pump stops working. Just make sure the bulkhead and connection will allow for a flow-rate at least as much as what your pump is rated for at the height you'll be pushing.
