How can you reduce foot pain, leg pain, and back pain while standing at work for a long time?

Breaks: Frequent breaks to sit and rest your back.

Orthotics/Shoes: You need to start with a pair of good supportive shoes. The next step is custom orthotics. These will align the feet, and the legs and back should follow. Think of your feet like the foundation of your house. Good foundation = good house. Properly aligned feet = good you!

Orthotics.: First you want good supportive shoes. You should not be able to "wring" them or fold them in half. They should only break/bend at the widest part of the shoe. A sturdy athletic shoe (not a minimalist style) will give you good support. If you're looking to beef up the shoes you already have, get a good insert or custom orthotic: you can use them to improve the shoes you already own.

Maybe Orthotics.: It sounds like you may have a biomechanical instability in your feet that is passing problems "up the kinetic chain." custom made prescription orthotics, made by a certified lab, under the recommendations of a podiatrist can help tremendously!

Many possibilities: Your pain could be as a result of many different things. A thorough history and physical exam and possibly some laboratory and radiology exams are needed to determine the exact cause. Causes of pain may include: trauma (fracture, sprain, arthritis), infection, metabolic conditions (gout), musculoskeletal or biomechanical abnormality and neurologic conditions (neuropathy).