Water Leak in pressure system

Hi I'm hoping there is someone who has seen this problem before.  My van was left when I stopped going out October last year, I'm now getting ready to go out the first time this year. BUT when I put water on the system to test everything out before my trip I found the pressure was not building in the taps and then water pouring out of the vent holes. I found the cause of leak underneath the toilet on the hose which flushes the toilet. The hose connection which is held on by a jubilee clip had pushed off the junction and obviously water was pouring from this hose.

OK so I put the hose back onto the junction and made tight the jubilee clip stopped the leak all working BUT on inspection I see the hose has moved on the junction and just a slight dribble, I've tightened the jubilee clip to its fullest extent and at the moment no leak and system is working. BUT I'm not sure why this pipe would come away in the first place and why the pipe has moved from the way I set it. IS it possible there is some type of adhesive which should be applied to the pipe.

Any information would be appreciated

Thanks

Harry Chopping.