How I transfer depends on the kettle I'm using. If it has a valve, I'll use the valve and tubing. If not, I'll pour it.
The kettles I have without a valve I only use for stove-top brewing (small batch or concentrated boil). If I do an outdoor brew, full boil and/or 10 gallon, it always gets transferred via the valve. Depending on the kettle, though, I'll transfer a stove top brew via valve.
If your strainer has rust, get a different strainer. I wouldn't use that one any longer. Or ditch the strainer.