Drain hole cleaning methods?

I ran water down the vent grill with a garden hose and used the wire to keep clearing the drain hole till crap stopped coming out.
It worked pretty well.

Of course this method would kind of suck if it really was rusted through, but it would also probably answer that question for sure.
If the drain holes ended up draining and you still had water leaking in, then you know you have some rust holes.