I had a question on this. Someone was explaining to me what the tritone sub was in jazz. Apparently its substituting the V7 for another dominant 7th three whole tones above the V7.

My questions are;

- does this mean that instead of playing the V7, i should just go up three whole tones and use that instead? In what cases can i actually do this, only in the context of a II-V-I progression?

- I was messing around with the keyboard and i was playing something in C#. When moving from the V to the V, my finger hit C# right before i went to the IV so it sounded like another 2-5-1 in the key of F# (which is actually the IV of C#). What is the theory behind this. It sounded really good and what chord do i use as a passing tone btw the V and IV if i do this.

I know it may be a bit confusing. I am at work and i had to get the answer before heading back home. :D