[Window Washers]

A picture would help loads.
Could well be in flushing mode.

agree or a video

[dd]

If I read the post correctly then fifteen metres is an awful long length of hose to run under pressure. 

Why? Water runs through 100m hose before it gets to my pole. It will also go through a very long water main before it gets to your house.

[Dave Willis]

Possibly, but if you stick yer finger over the end of a long garden hose you can shut the water off without too much effort. It's not like it's being pumped in the same way.

[Timmy Boy]

Many thanks all, I will take a picture and post it. I will look for the flushing valve as I have not seen/checked this and let you know. I used the fitting kit from streamline to go from the hosepipe down to the thin white pipe and then the same when going out.