Read the other question went to the web sight about rust in iron pipes
This is not rusty pipe but iron (slime) buildup in 1&1/4 plastic pipe from pitless adaptor to pressure tank in basement

Hey Steve,

Rust Away may be the product you're looking for, click on: Rust Control - Interstate Products, Inc.
Fill the pipe with Rust Away and just follow directions. After you lrt it work and the slime is dissolved open up the pressure side and pump it clear. Good luck, Tom