Trap Dri Moisture Control Trap prevents excess water escaping from your water trap into your pipe bag by capturing and retaining moisture in the tube to be emptied. Trap Dri is fitted to your existing water trap tube and does not require a zip bag as it can slip through almost any split stock. The trap works by collecting water which condenses inside your water trap tube and locks it inside the Trap Dri. Using the Trap Dri in a natural or synthetic pipe bag will help your pipes to remain in tune for longer periods of play. Virtually maintenance free, just simply remove every few weeks to clean.