I'm updating my bathroom. I currently have pipework for my sink just coming through the floor in 15mm which then reduces into 8 or 10mm pipes. This fitting is just above the floor and I want to avoid altering pipework under the floor. Is it OK to then change the 8 or 10mm pipework back into 15mm with a soldered fitting which will then go to my new sink. So pipework will be 15mm then a small section in 10mm the back to 15mm. Hope this makes sense lol.