You can use an overflow box. Thy hang on the top a siphon the water down to the sump. Your tank should only have tempered glass on the bottom the sides should not be tempered they would be to rigged and brake under the water pressure, or if a rock it it it would shatter dumping 100% of the contents on the floor, where regular glass would crack and leak much slower. So it would be odd if the front back and sides of your tank were tempered.