Blow loose debris from the grooves of the boards with an air compressor. While doing this, wear eye protection to shield your eyes from flying debris.
Brush out the tongue and grooves of the boards with a nylon bristled brush of medium stiffness. Different sizes of brushes are useful, depending upon the size of the tongues and grooves. An old toothbrush is good for this.
Mix a solution of water and wood oil soap cleaner in a bucket according to the soap cleaner manufacturer's directions.
Clean the tongue and grooves with the water and oil soap cleaner solution. To do this, dip the nylon bristled brush into the solution and use it to brush out the tongue and grooves. Repeat after rinsing the brush until no more dirt comes out of the wood.
Wipe along the tongue and grooves of each board with a clean rag dampened in a fresh solution of water and oil soap cleaner.
Let the boards dry completely before using them.