Step 4 · Snake the Branch Drain Line
Since the gurgle persists when other fixtures are used, the clog is likely in the branch drain line beyond the toilet. To access this, you must remove the toilet. First, turn off the water supply using the shutoff valve behind the toilet. Flush it to drain the tank and bowl. Use a sponge and bucket to remove any remaining water. Disconnect the supply line from the tank. Use an adjustable wrench to remove the nuts from the closet bolts at the toilet's base. Gently rock the toilet to break the wax seal and lift it straight up. Set it aside on an old towel. Now, feed a medium drain snake (25-50 ft) into the exposed drain pipe in the floor. Push the snake in until you feel resistance, then lock the cable and turn the crank to work through the blockage. You may need to move it back and forth. Retrieve the snake, cleaning it as you go. This should clear the shared line.