Basin Waste to P Trap

[Thisis]

I bought a sink waste with a G1¼″ BSP thread, I cannot figure out how to connect it to my P Trap. The P Trap has a 32mm compression connection, it sort of fits but the threads aren't right.

At first I thought it was that it needed a 40mm connection but this didn't work. I picked out the new waste by measuring the diameter of the old one, 40mm.

It was set up like this by the plumber who installed the bathroom, with a metal connection of the sink waste going into the 32mm P Trap but it did always leak. So maybe I am trying to replicate an incorrect setup?

Do I just need to switch to a bottle trap, get another waste, or is there an adapter?

 

[CountryFan]

Are you trying to fit a basin trap to a basin waste or sink waste to sink trap or a mix of the 2? Any photos?

 

[foxhole]

Post is a bit of a mucking fuddle , pics would help . Assuming you mean basin ? P traps only have a compression fitting at one end , the other is threaded with a nylon washer to attach to basin waste .

 

[Thisis]

Yeah sorry, this is in a bathroom, this is the P trap:

and the waste:

 

[denso13]

The threaded bit on the trap should screw on. Looks fairly standard to me.

 

[terryplumb]

Looks fairly standard to me too. Is the seal in the trap in good condition ?

 

[Thisis]

Yeah I thought it might be the trap that was the issue and bought a new one but I'm having the same problem where it looks like its going to screw on but it pops and comes off. I just can't seem to catch the thread, is it possible its slightly off or do you sometimes have to turn it a lot before it works?

Edit: I took it back out of the sink and compared it to the old one, turns out the measurements must be slightly off. The pipe can sit into the old one, but the new one is slightly too small:

Is there some difference in sizing I should be careful about? The waste I bought was: "Universal Fit – Standard G1¼″ BSP thread (φ40.5 mm), fits most UK basins." (Ibergrif M20502 )
The P Trap is a "McAlpine Adjustable Inlet Tubular 'P' Trap White 32mm"

 

[terryplumb]

As long as you are not cross threading the plastic nut ,it's highly unlikely that 2 traps are the problem . The trap should screw on easily. You may have a European waste fitting that is not a BSP thread.
*******
Edit ,just seen your added pics ,and it's now obvious that the inner diameter of the waste fitting is too small.
If it's a small difference file some off the trap.

 

[Madrab]

Does the spigot part of the flange actually fitting inside the throat of the waste? I have seen this with some 'universal' waste's before whereby McAlpine traps with that spigot type flange doesn't fit inside the waste, therefore the trap can't tighten up. I've had to trim the plastic to get it to fit into the waste before now.