The threaded part of the waste (a chrome click clack type) seems to be about 38mm external diameter. but is too narrow for the thread on a std plastic bottle trap thread to grip.
With it there is also a smooth "extension tube" (10 cm long, non threaded about 31mm external diameter) which can screwed onto the bottom of the waste.
Not sure where my inlaw got it from - Generally, it looks to be good quality... but as I said doesn't seem to fit the std bottle trap...
I wonder if its some sort of continental fitting? And Ideas on the simplest way to connect it up?
thanks for your help AJ