Wood-oil which is boiled linseed oil mixed with a carrier such as white spirit, makes a good sealant-preservative. If you buy a ready mixed version make sure the oil content is 35% or better.
As a by-the-by, never use a pressure spray on timber decking as you destroy the cell structure of the wood. There are attachments that clip onto the spray lance that enable you to give the deck a good scrub, usually back to the original natural tone, after drying apply several coats of the mix, drying in between.This should be good for a couple of seasons if fully exposed to the sun and weather.