what does the idiom "dragging the line" mean?
its from a Tommy Jones song

Here you'll find the lyrics to the Tommy James song "Draggin' the Line":

http://home.att.net/~bubblegumusic/songdraggin.htm

Here's a speculation about what the phrase may mean:

"I seem to remember my older brothers having this discussion with a
friend of theirs who worked on a barge on the Ohio river. Aparrently
draggin the line was a reference to some work that took place on the
barge such as pulling ropes. Therefore the song is talking about
making it through your day by day existence with a positive outlook."

http://www.onehitwondercentral.com/forum/thread.cfm?threadid=2886&messages=4

It is a reference to snorting cocaine. You've seen movies where they
line up the cocaine in little strips on something and then snort it up
with a straw. They are called "lines" of cocaine. Hence, "draggin' the
line".

Read the words to the song and you can see this is what it is talking about.

Tommy James had other drug songs also such as "Crimson and Clover".