Do you know that you do have water in the rudder or are you just asking about the idea?
If you have water in the rudder, then it would be a good idea to drain it.
Question is...how did it get there?
I have some water in my rudder and I've drilled a small hole near the bottom. It is weeping some water.
Next spring, I plan on cutting out some of the rudder where it meets the rudder post (a bevel) and then use 5200 to seal it up tight. I may try to get some thinned epoxy to flow down into the rudder along the post prior to sealing up the joint.
BTW, not a PSC but I do have a foss foam rudder. Does PSC use the foss foam rudder or similar?