I use the 12" spacing, and the spread of the water is good enough that if I have to plant every 6", it's fine. You can find it in 100' and 500' rolls. I like it for my onlons and beans, peas, things that are planted closer together. I don't use it for my larger crops, tomatoes, zucchini etc.

Here is a link that might be useful: Drip Tape

I got mine from Drip Depot - http://www.dripdepot.com/product/4596fd8075eb512997600000

You can choose spacing. I like it so far except I didn't get anything to plug up the end so I'm having some issues with that. I would recommend getting ends for it when you buy it :)

dz,

At the end fold it back on itself and rubber band or paper clip it.
When you want to flush remove the band. JMHO Aloha