Since the 20th century the bass drum part has been written on a single line with no clef. This type of notation became standard because the drum has no definite pitch.
In jazz, rock and pop music the bass drum part is always written at the bottom of a system.
In older works the bass drum part is usually written in bass clef on the A3 line, or sometimes as a C3 (like the tenor drum).
In old scores the bass drum part often contained notes with two stems. These indicated that the note was to be played with the drumstick and the switch simultaneously (the switch is an older and less commonly used form of “brush”, normally consisting of a bundle of twigs tied together).