Turning Pico-reef into a refegium

[MoodyManticore]

So I have one 126 liter display tank (30gallon) and a 25 liter Pico-reef (5gallon)

I'd like to turn it into a refegium without drilling glass, I've looked into tubing and overflow boxes, but I'm unsure of how to make one without risking flooding my kitchen.

One idea I have is making a sump behind the Pico-reef that pumps water between the tanks?

(Also I've been switching water from the display tank into the pico reef twice a day, should I stop or am I helping somewhat)

 

[Seregus]

If it was me, I would consider different options, since I had a 30g and made a sump and used overflow box back in days (no drilling).

1. Add a sump to 30g and get rid of pico and set refugium in this sump. This could be done with nice overflow box, some are even self priming if not left to dry out for extensive time, like a day. Maybe Tunze one? And pump in sump.
2. Use pico as a sump - same as above add overflow box to main and pump to pico, done.
3. Install pico above display, install overflow box in pico and add pump in display.
4. Add a sump and use it for both pico and display. Means two overflow boxes and a bigger pump.

The biggest benefit for having sump is to move equipment from display and pico into it, could have one heater for both one auto topup for both… but it means money and space.