On Apr 20, 11:39*am, "Karl Townsend"
wrote:
My fittings on the six inch underground irrigation system are rusting out..

... I'm getting a small rust hole right at the bottom of the
pipe where water sits during the off season.

So, why not drain the pipes, then put a vacuum pump on 'em to dry
those last bits? The brown cruddy type of rust needs water and
oxygen to form, and you can remove both.