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Pour 2 gallons (3.78 l) of warm water in a 5-gallon (18.92 l) bucket. Add 2 cups (400 g) of powdered oxygen bleach and mix the solution together using the sponge or brush that you'll be using to scrub down your deck. Continue to mix the solution until the components are well incorporated.  Remember to wear water-proof gloves, boots, and possibly rain pants when working with bleach. Mix the solution outside or in a well-ventilated area. If you don't have a deck brush, you can use a large porous sponge to scrub down the surface of your deck instead. Liberally saturate the surface of the deck with the solution, then start scrubbing the deck until the solution starts to lather.  Synthetic deck brushes can be purchased at most hardware stores and are designed specifically to wash a deck. Be careful when walking on your deck because the bleach solution will make it slippery. Letting the suds sit on the deck will allow the oxygen bleach to absorb the dirt and algae on your deck. It's important that you don't let the solution thoroughly dry on the deck, or it can leave a film on the surface. Use the hose to do a final rinse down of your deck. If you don't have a hose, you can get buckets of water from an indoor faucet and use that to rinse down the deck. Make sure that all of the bleach solution is rinsed away before letting your deck air dry.
Mix warm water and powdered oxygen bleach into a bucket. Scrub down your deck with a synthetic brush or sponge. Let the suds sit on the deck for 5 minutes. Rinse down your deck.