I would like to replace the sewage pipe (running from the toilet into
the floor outside the house) with white pipe and fittings as A) i've
painted the back of the house white, B) it looks old and scruffy even
though I've painted it white (lots of old paint on it), C) one of the
joints is weeping a bit and has been repaired many times before
(bodge?) and D) i've got a new toilet to put in but also I want 30mm
insulated plaster board on the wall so the toilet will be moved out a
bit and the existing pipe may not fit.

Anyway the questions a is white pipe and fittings/joints available,
is plastic suitable and the biggie - the old metal pipe just
dissappears into the concrete floor outside - is it likely I can lift
the old pipe out of the floor and just put the new plastic stuff in?

Am I likely to run into big problems?