By clean do you mean change the water? Or do you mean clean to disinfect it before filling it?
If the former you will want to get a water siphon. You can get these at any pet store as well as walmart. You can google videos on how to start it..personally I just suck the end to start suction. You can also make your own siphon out of air line tube (also bought at a pet store), but the small diameter of the hose will take you longer to siphon the water.
You will want to take out 100% of the water each week until you begin cycling (you can search the forum for more information on this). Once you start cyclingyou will do partial changes.
If you want to keep the tank uncycled you will do one 100% change and another 25-50% change each week, each time siphoning the bottom to remove uneaten food and waste.
If the latter... to disinfect a new tank all that is needed is to rinse everything with scalding hot water and to let it dry before filling it. If it is a used tank rinsing it with a 10% bleach solution and then rinsing well with hot water will do the trick.