If you like watersports, you should take a look at this harness with funnel.
This sturdy head harness is made of 20mm wide and 3mm thick rubber, and fits perfect.
Outside is an attached large rubber funnel, inside a hollow mouth gag.
Optional the buckles can be equipped for locking with padlocks.
The harness colour ist black, but you can choose the gag colour.
The harness fits for a forehead circumference of 52cm to 62cm.