Damp proof course (joining old DPC)

Im nearing putting the floor in my extension, and I know I have to join DPM to house damp proof course. The new floor will be lower (2") that existing DPC. Do I chase out some of the old DPC (1"), put down a layer bitchumen or something and lap DPM on to it and cement back up, or is there an easier way that BCO will accept ?, and while im at it, do you just join around pipes etc that come through DPM with gaffer tape or something ?
Many thanks in anticipation

 

When you say use a paint on bitumen product ? Do I just paint brickwork upto DPM and overlap up wall side, as this is what I have been told, but its my house so I want it right, Many Thanks.