Swimming pools blog

Hi all,
I am fitting a new 0.030″ vynil liner to a concrete lined indoor
pool and require information of when to cut and fit the drain hole,
I understand that when the lamp, inlets and skimmers part of the
liner is cut away water has to be up to that level, but as the drain
is on the very bottom how and when is this part of the liner cut out.
I assume that the beading is clipped in all the way around first,
then the water put in and a vacuum cleaner is used to suck the air
from behind the liner as it is filling. the liner perhaps swept with
a broom to iron out the creases.
can anyone help me with this question,
One further point my old liner was very old and was put directly in
contact with the rough concrete,can a backing underlay type of
material be applied to the concrete fist, perhaps simular to an
underlay that you use under laminate flooring ,a thin 1mm - 2mm

polestyrene sheeting, or a felt?
many thanks in advance.
Barry