I have been getting two weeks with my Dexcom G5 for the past year with the following methodology. After showering I clean my arm with rubbing alcohol. Then I use skin tac to wet the entire adhesive pad, on the sticky side only, and wait a minute for it to dry slightly. Then I bend my arm so the skin stretches and have my wife or kids smooth out the adhesive so that all the edges are stuck to my skin.
After it is completely dry the G5’s cloth adhesive material has a hard feel. I swim three or four days a week and have not had any issues since using this method. I have also tried going into week three on three occasions. All three times I felt that the readings were becoming inconsistent. Also, the effects on my skin were negative in comparison to the normal two weeks.