Replacing basin waste

[mjd]

Following a leak from the existing waste outlet on our bathroom basin, I successfully managed to destroy the existing fitting by over tightening the centre pin in an effort to stop the leak. (Lesson learned).

I am looking for a suitable replacement and am not really sure with regards to sizes.

The original fitting had a 40mm trap connected to it directly by way of a compression type fitting, and itself measures 40mm. All existing waste pipe is 40mm. All the basin waste kits I can find online so far are 32mm?

I know I can convert 32mm to 40mm,but is it likely that a 32mm basin waste is going to be too small for my basin?

 

[mjd]

I have checked few more measurements.

The original fitting used a centre pin to secure a plastic flange and washer to the bottom of the basin. The outlet of this fitting was 40mm and a 40mm bottle trap connected directly to this.
The hole in the basin itself measures 40mm.
The 'plug hole metal bit thing ' measures 62mm in diameter.

This arrangement hasn't leaked in the six years we have been here prior to today, so I can only assume it was OK.

Based on the measurements above does it sound likely that a 32mm fitting with a 40/32 reducer would do the job?

 

[mjd]

Thanks for taking the time to getting those measurements. The schoolboy error was the bit that threw me
The pipe is 40mm throughout as it takes waste from the bath,basin (downstairs bathroom),dishwasher,and washing machine. Its a ridiculous setup put in by the previous owner who was a bit of a DIY disaster in general. When we finally get onto sorting the bathroom and utility, I'll run separate pipes for the bathroom and utility. The amount of congealed gunk I have found in the fittings I have removed so far is pretty gruesome. Its clear that waste water from the utility is finding its way up the wrong pipe which would explain the gurgling in the basin when the washing machines discharges into the pipe