This Buon Vino 3-piece airlock is a very popular design. It is easy to clean, easy to fill, and easy to use.
The center tube has an unobstructed opening which helps prevent it from getting clogged up with an active fermentation.
If you want to use it as an adapter for a blow off tube, you can connect 1/2" silicone tubing to the center riser and run it into a bucket full of water.