The safest way to prepare LBTR for the reef aquarium is to blast the junk off. Any organic matter left on and in the rock requires time to decompose. 

 Though at various times I have not been so meticulous. Even with blasted LBTR, on occasion I have seen dirty sand slowly spill out of it after it has been in my tank for a few days. It seems that the action of critters finding homes in the rock pushes dirt out.

Still, a major focus when introducing anything into the reef aquarium is the avoidance of dieing and decomposing matter. Anything we can do to prevent the need for "cycling" time can only help the tank get going.

I even recommend the practice of moving LR from one tank to another, completely submerged in saltwater. And when placing purchased LR into the tank, twist, turn and shake it to remove air bubbles that would otherwise kill the life living in the pores of the LR.

Oh and FYI, soaking can be useful but don't waste time and money with chlorine bleach. Bleach can actually cause problems on the other end, after it's added to the tank. But even after soaking, the rock still needs to be blasted. And since blasting unsoaked rock effectively removes most of the organic matter, I don't really see the need for soaking.