There are 2 Block drains, mid ship of engine (just in front of the starter on one side,down low. Two Manifold drains , end on manifolds aft end on the boat. Hose clamps should be for the sea water pump on the front of the motor, also check the lower hose on the circulating pump to make sure they did not remove it, also a small hose on the fuel pump.
Be careful to make sure that the sea water hoses are on correct as they are the same size & if crossed you WILL burn up the Impeller.
Your Volvo owners manual has great pictures of where all go & hose routing. When you back in the water or flush raise the motor hatch & do a visual to make sure that all is well. REMEMBER that if the sea water pump is not working that the temp gauge will not register until it is to late.( no water in the block ) I recommend that you let the engine temp come up before leaving the ramp.