Customer called us out for a back up in the master bathroom. On arrival I tested the shower and sinks. The sinks started to gurgle but not the toilet. I recommended running a tub gun through the shower drain to clear the blockage. Customer agreed. I ran the tub gun through the shower and successfully cleared the blockage. I tested the drain by running the shower and sinks. I then cleaned the shower. Customer did have cast-iron outside but wanted to call us out on a later date.