I decided yesterday to flush out my fresh water tank on our Hymer 564, and so filled it up until the LCD display said it was 100% full. I then went inside the motorhome and turned on the taps. After much spluttering some water came out but it certainly wasn't pouring out as it should. i then went outside the motorhome and I saw that water was pouring out of a pipe located toward the rear of the vehicle. I have looked in the manual to see hat this pipe is but can find no reference to it at all, but needless to say it carried on pouring out even with the taps inside turned off, until the tank was empty. Studying the manual again today I read that there is a safety system that opens a valve when the temperature goes 8 degrees or lower. According to the manual, this valve is close to the waste water tap. I had a look and found the valve, opened it and water started coming out. I assume that this was water from the boiler. The main flow of water yesterday was not from this valve but from a pipe on the other side of the van which seems to be located under where the boiler sits. There seems to be no tap for this pipe. I'm confused as hell by this and no matter how much I read the manual i can't seem to comprehend why the van would dump all of the water for no apparent reason. Anyone got any ideas?