Washbasins

How to install a washbasin:  

If you wish to install an inboard ceramic wash basin, buy your washbasin, before making the slab to go around the washbasin. Seal the join of the base of the washbasin with the slab with silicon. 

The drainpipe fitting that leads away from the washbasin should be measured from the diameter of the hole of the washbasin, which has been designed to be compatible with the common plug/drain sizes.  Again, seal this join with silicon.