To determine the asbestos-containing materials in a bathroom, is it enough to take one sample during the asbestos survey by drilling at a random place through a tile seam, collecting the powder and analysing the powder?

Sampling must cover all structures that will be taken apart. Sample analysis or other analysis must be done on all the materials that will be removed. The result from a sample piece is more reliable than from a drill sample. This requires expertise from the surveyor.