Our toilet is located next to our standup shower. Each time it rains, the toilet backs up into the shower! We have plunged them both back and forth and poured in rid ex as we were told by the landlord but it is still not working. Therefore the shower floor is filled and running over onto the bathroom floor. We did get the toilet to flush but the shower is still backed up and when we flush the toilet it backs up into the shower. HELP PLEASE!!

Each time it rains, the toilet backs up into the shower This tells me that you have rainwater run off connected to your sewer and it's causing a problem.
In my area this is illegal. Have the line snaked and if tyat doesn't help I would disconnect the rain water line and run it out on the ground. Good luck, Tom