moopy
To be honest it looks like a cobbled together affair. When you take out the off white piece there should be a black o ring. I guess this has failed in some way. To be fair this arrangement is not meant to be as macerators are only supposed to be used with copper pipe or glued together plastic pipe (solvent weld). I guess there will be some form of adaptor from the small 21.5mm pipe below to the large white couple. Take a look at this from screwfix http://www.screwfix.com/p/straight-coupling-32mm/11632
I strongly recommend that you get this system re-piped immediately.
