Depending on the type of work, i would never reuse my magical candle scraps. I look at them as garbage and spiritual byproduct that is ready to be returned to the Universe. Now, i'd accept the argument that religious devotional candles are fine to reuse, like candles for the elements or other altars, but for me, spellwork candles are "used up."
If your candlework is to draw something positive to you like luck, money, a new lover, etc., i'd bury the remnants in a potted plant by the front door. If that's impossible, i'd put a flake of candlewax under your front door mat and then bury the rest by the bushes/landscaping at the front door of your apartment complex.
You have to be a little sneaky and quick about your work. Burying spell remnants in public is best done at night, although sometimes your best cover is in full daylight and in full view of everyone - people can be less apt to think you're up to something if you're doing it in full display.
If your candlework is for removal or separation, like working through an addiction, bad luck, cursing, cleansing, etc., i'd dispose of your candle remnants at a crossroads, any place where two roads meet. Take the remnants in silence to the crossroads, leave them either in the middle of the street or at the street corner, turn around and walk away without looking back, and go home a different route. I have a friend who lives in New York City who has a regular disposal spot in a large flowerpot situated at a busy crossroads intersection. She buries stuff there regularly. Again, you have to be discreet - working at night is best.