Start with a tissue sample.
Place it in a salt buffer -- a saline solution made from purified water and non-iodized table salt. Add a little bit of meat tenderizer (it's a protease) and some shampoo (contains sodium dodecyl sulfate; you want about a 1% solution of this, but you'd have to determine that empirically) and allow to sit at room temperature until it turns into a slurry of formerly tissue, now digested goo.
Place this in a centrifuge -- a salad spinner should work nicely -- until you've separated out the solids from the liquids. Decant the liquid into a separate container. Add a concentrated salt solution so that the final molarity of sodium is ~1M. (You need a high ionic concentration.) Add isopropyl (rubbing) alcohol, about 1.5-2x the volume of the existing solution.
You will see a white stringy precipitate. This is DNA.
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