I am thinking of making a berlin sump. I will be using an eshopps overflow box do I do not have to drill into the tank. My question is the eshop box flows 200gph. So will I need a stronger submersible pump to get the water back into the tank? or is a pump that is 200gph sufficent enough?
You want a return pump that will put out less water than the overflow. If the pump is faster than the overflow, you drain the sump. The overflow, on the other hand, can only take what water the pump puts into the tank, so it can keep up. So you want the pump that will put out around 180 GPH at whatever head loss gravity gives you. A great head loss calculator:
The concept of an overflow is that the water in the main tank is at the exact level of the overflow box. When water is pumped up from the sump, the water in the main tank overflows into the overflow box. Therefore, the drain pipe can not drain water faster than the pump can pump water up.