This is how I do mine - turn off the outlet tap, turn off the inlet tap and quickly turn off the power. Leave your hoses in the water. Open up the little airhole thing at the top, undo the clips on the side and lift the lid off. If you don't open up the airhole its still airtight and you can't get the lid off. Take the baskets out and rinse them out in a bucket of water that you have already removed from the tank. Rinse out your sponges and filter wool in the same water and if you have to replace don't replace too many at once. If theres a lot of crap in the main part of the filter you might want to chuck it. Put baskets back in and refill with more water from your tank. Put lid back on and top up with water. Close airhole.
Switch on, quickly turn on your inlet hose and then your outlet hose and it should run as sweet as, otherwise you can always give your outlet hose a good suck on to pull the water through.
Others might disagree with the fact that I turn the power on and off when I do, and the order I turn off the taps but this makes sure that there is water in the hoses at all times.
However if you have to clean your hoses you will have to dismantle and refill them before you turn everything back on like when you first started it up. Good luck