Hi, the Bell and Drum Towers is near Guloudajie subway station.
Two itineraries for you choose:

1> Take Line 1 from Dongdan to Jianguomen (passing 1 stop), then transfer to line 2 from Jianguomen to Guloudajie (passing 6 stops)
2> Take Line 5 from Dongdan to Yonghegong (passing 5 stops), then transfer to line 2 from Yonghegong to Guloudajie (passing 2 stops)