When Tom Sawyer's aunt wanted to preserve her fence, she had Tom paint it with a coat of whitewash. Today she might have had him use a fencing preservative or water seal product. Although today's pressure treated lumber is more hearty than what Tom's aunt would have used, a coat of waterproof sealant helps preserve the wood's colour by preventing water from soaking into the wood like a sponge. A waterproof sealing agent can also help prevent wood from cracking and splitting.
Put on protective clothing, goggles, gloves and a breathing mask to protect you from airborne particles of the sealant.
Pour the sealant into the reservoir of the garden sprayer and cap it.
Pump the sprayer's pressurised spray lever to create pressure within the mechanism.
Spray the sealant over the fence, working in even strokes with the grain of the wood.
Brush over the fence with a paint brush to work the sealant into the wood.