It's difficult to see clearly what type of pipe it is. yYou should be able to get a connector from a DIY shop or caravan dealer. Probably a push fit but you could put some silicon sealer on the joins.
------------- DS-There's more to life than football!!!
Generally, as DaveS rightly says the drain pipes are only push fitted. This may be because it is quicker to assemble in the factory but that fact does make it easier to fix a blockage. It looks to me a bit there are some bits missing, an elbow and/or straight bit of pipe to connect with the external drain socket.
Dave.
------------- Give a man a fish and he will eat for a day,
Teach a man to fish and you can get rid of him for a whole weekend.
That looks to me as though on the right hand side of the leak you have a corrugated waste pipe and on the left side a rigid waste pipe and where the two join, it is leaking. These pipes are just joined by a push fit connector which may have just jiggled apart over time as the caravan bounces about when being towed. In that case, all it may take it to firmly push them together again and as has already been suggested, a bit of sealant might prevent it coming apart again too quickly.
A good clean of the connector some sealant on and push it back firmly. If the flexible pipe is split or damaged its easy to buy a length from a caravan dealer or DIY place and replace it.
------------- DS-There's more to life than football!!!