Is it ok to continuously drive in the left lane?
No, according to RCW 46.61.100. Upon all roadways having two or more lanes for traffic moving in the same direction, all vehicles shall be driven in the right-hand lane then available for traffic, except (a) when overtaking and passing another vehicle proceeding in the same direction, (b) when traveling at a speed greater than the traffic flow, (c) when moving left to allow traffic to merge, or (d) when preparing for a left turn at an intersection, exit, or into a private road or driveway when such left turn is legally permitted. On any such roadway, a vehicle or combination over ten thousand pounds shall be driven only in the right-hand lane except under the conditions enumerated in (a) through (d) of this subsection.