If you have a clogged toilet and shower drain, it is likely the blockage is located somewhere further up the sewage line. If you have tried to unclog them both using conventional methods and nothing is working, you should not try to unclog the sewage line on your own. Instead, call a specialist who will be able to do it for you, as the steps for how to unclog toilet and shower drain could require major works to remove the obstruction and / or repair the sewage pipes.