Before you attempt to remove the basin obtain drain cleaner from caravan accessory shop & or drain flexy wire cleaner which I think is best used by at the outlet end due to the right angle bend in most basin/sink drain outlets (check if you can see it).
Not same van but I can access mine and pull off the pipe together with rubber seal. Using the cleaner block the outlet with a cork or rag follow product procedure.
Then fill basin and drain off in most cases this will free a blockage. Run the flexy drain cleaner through pipe as far as it will go do same with the kitchen sink.
You could contact the caravan manufacturer they will tell you how its fitted if you still need to remove it. If the above makes no difference then its a remove the pipe job which could be easier than removing the basin and fit new pipe but take piece of pipe with you to get the right size and new screws for the support brackets plus a couple of brackets in case you can't get screws out and have to cut the bracket. Lower the caravan on the front as far as you can and lower rear corner jacks even on blocks to if er intdoors gets in while your under it it won't tip heh! heh!. This warning is I have one who would get in without thinking.
ABI Caravans ABI Caravans Ltd Swinemoor Lane Beverley Humberside HU17 0LJ
Tel:01482 862976
bob, August 2011
