The best solution to unclog drains or get rid of smells that come out of the shower or sink is to use Potasa
When working with chemicals, use gloves and a breathing mask. If you decide not to use either precaution, keep your face at a distance to avoid breathing in fumes or getting chemicals into your eyes.
For every drain that has an issue, place entire 300 grams bottle on top of the drain. If possible get hot water from the faucet and place a 1/2 of cup or 65 grams of hot/warm water on top of the Potasa. You don’t want to saturate it with water just enough to wet the Potasa so that it slowly starts going down the drain. We need little water (1/2 cup of water) so that the Potasa maintains it strength in high concentration. Too much water will dilute the Potasa’s strength.