Best samples are large samples taken as a plate across the log.
Though the oil tend to smear with the drill cuttings and prevent it from getting out around the borer.When you take out the borer, the core is often left in the middle of the hole in the log.When building or repairing houses, grooved parts of a board are now and then cut away.(From tongue and groove boards.) I cut them into 30-40 cm long pieces and save them for storing cores in the groove.After you have collected some cores you have to mount them on some sort of wood strip.
I prefer something with a cross section like 8 * 20 mm.
You need something to cut it at the bottom so you can take it out.
I use a metal strip which is bent at the end to work as a knife.
) An increment borer can also be used in old wet wood like a water-soaked log.
The increment borer is used with a long metallic strip, an extractor.
That's your chance to get several samples from the house!