I am in the middle of doing my kitchen, and when i went to fit the sink i discovered that the waste fitting under the sink, internal measurment was 39mm, and the trap fitting external measurment was 40mm. I thought it was all standard sizes. Can someone please advise.
Assuming you are saying that the trap flange will not fit into the waste either file or trim the waste so it does fit or go and buy a new waste of the right size. Do not try reducing the size of the trap flange.
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