20 gallon established aquarium, wanting to add a refugium

[impreza]

hi, i have an established 20g fowlr, i want to add a refugium. Is there any way of adding a refugium to my tank? i have a spare 10g tank that has no use. My 20g doesnt have an overflow either which is the problem i am facing as i cant see how i can add a fuge without an overflow.
thanks

[Gogeta]

I would place the 10 gallon above the 20 gallon, somewhere that could hold it. Then just use a pump to pump water from the 20 to the 10 gallon. Then try to find someone that would drill the 10 gallon and put a bulkhead in it going down to the 20.