Caulking: Remove old caulk. Spray with bleach diluted to 10% to remove any mold. Fill tub with water. Place tape 1/4" from crease. Squeeze deep into crease. Smooth out with wet finger. Then peel off the tape immediately, before it dries. Drain the tub when caulk is dry. Wait 24 hours before using tub.
How to caulk a perfectly straight line: 1. Squirt some caulk in the area between the tape. 2. Smooth caulk with your fingertip. 3. Continue smoothing. 4. While the caulk is still wet, slowly and gently pull up the tape. If you wait until the caulk is dry then it will come up as well.