Most I know are push fitted and the only way is to either cut if enough slack or warm the pipes up with a hairdryer sometimes works making the pipe soft and easily removed.
If you have to cut the pipe check with local caravan dealers shop for push fit straight connectors for the blue and red water pipes, explain why. the push fits are similar to the domestic ones but the domestics only work with copper tubing. DON'T stick you finger in the joint to test you'd have to get it removed surgically, no not the finger, the joint!
bob
May 2013