Put empty needle in your right hand, your stitches-filled needle 1 in your left hand. Knit/do pattern across needle 1 until needle 1 has no more stitches, and the empty needle in your right hand is full. Switch the empty needle 1 to your right hand, and put stitch-filled needle 2 in your left hand. Again knit to the end of needle 2. No more stitches? Put empty needle 2 in your right hand and grab full-of-stitches needle 3.
Keep going like this. You'll get a lovely tube in whatever pattern you're making.