To fill a caravan tank you need to feed the water gradually.

This is so there is a gap for the air to escape. 

If you attach something like a hose to the tank and fill it under pressure without allowing the air to escape, the pressure will become too much and cause the tank to explode. 

This will happen even if you have a breather on the tank if the force of the water is too high. 

When you fill a tank under pressure it will explode.  Unfortunately, as this is the incorrect way to fill these tanks it is not covered by the manufacturer's warranty. 

We recommend getting a water tank filler to connect up to the tanks to avoid this.