Hi Gaz, this is the one by Reef Octo, you would be able to get it from any Reef Octo stockist, believe it is about 400 bucks, might be wrong though! You not going to be using the built-in filter then, so just cut a hole in the back of your canopy where the filter used to be!
Instead of drilling a tank, just an idea which has worked well for me and my 700l tank, I installed a 2000Va UPS, purchased for R 2020.00 from local computer shop. This gives my gravity fed sump, return pump of 2400l/h or 35 watt, 3hrs run time in the event of a power cut, the alarm company calls me if there is a power cut, I then know I have 3 hrs to get home. The expensive way is to put valves in at R3000.00 a pop. Hope this helps.
Other option is to have a sump that's above the tank. That way you need a pump in the tank (or next to/behind if you have it "suck" through a pipe) and an overflow on the sump that goes back down to the tank.
Thats what i am using, with a home made skimming box for the return pump.
So if the sump breaks, the pump wont empty the display tank.
Just make sure the sump does not overflow the display tank if the power fails, therefore a 20mm water level must be maintained below the rim of the tank.
The auto top up system sensor is then in the display tank, and its level is kept constant with RO.