Try brushing your inner cheeks with a soft toothbrush before letting saliva collect in your mouth for your sample. Once saliva collects, swish the saliva around in your mouth before spitting into the test tube.

The test I and family members took, 7 and counting, used cotton swabs and instructed us to rub them against our inner cheeks to collect cells.

We had no failures. We used family DNA.com

Good luck.