Drill holes in the corners of the square you’re cutting out for the sump to fit into. This will make it easier for you to cut out. Put on your safety glasses, gloves and ear muffs and use the angle grinder to cut out the square in the fibre cement board. If you need to, use a hammer and chisel to help you remove the fibre cement board. With your battery powered saw, cut the next layer of flooring. You may need to use a handsaw to complete the cuts to the corners. Lift this piece of flooring out. You may also need to use the handsaw to cut any under-floor insulation that might be there.