The mouthpiece has been designed to fit inside the mouth with a retaining flange, and bite blocks for the teeth to grip to ensure an adequate airway. Consider the size of the mouth and what is a comfortable gap for the teeth and estimate the size of the mouthpiece accordingly. It is known that undue pressure on the bite block causes strain at the lower jaw joint. Bite blocks are to rest the teeth against not chew on and clearly the more robust they are the longer they will last. However, if oversized they will cause discomfort.
All snorkels are of similar dimensions to allow both ease of breathing and clearing.
Some snorkels are now fitted with a purge valve to allow water to drain from the bottom of the tube rather than be ejected by blowing. However the seals of such snorkels can leak if grit or sand fouls the outlet. Sealing the top of the tube with your hand and forcefully clearing the one way seal, thus flushing out any debris, may clear this. A variety of ingenious methods have been devised to attach the snorkel to the mask strap including a sleeve or clip or quick-release attachments. Snorkels are available in ranges of colours to match the mask.