If the rust cannot be easily removed by wiping, you can use diluted phosphoric acid: it's as efficient as Evaporast, but much less expensive. I buy Phosphoric Prep & Etch in hardware stores, add water (2 parts of acid to 1 part of water) and use the solution to derust steel and cast iron in my machine shop. Amount of dilution is not really critically important: I used the stuff without any dilution as well as with more water. The 2:1 proportion is what I found reasonable, and the spent solution can be reused many times. Just make sure there are no aluminum parts or certain decorative iron oxide finishes: they will be damaged (the same is true for Evaporust): aluminum surface will become etched when you keep it in long enough, iron oxide finishes will disappear (some of them almost immediately). After all, rust is also one of the iron oxide forms. At the same time, the black oxide on the bolts or drill bits is, usually, not affected. Try to fully submerge the parts to avoid black line at the solution-air interface.
Depending on the amount of rust, the process will take from about 10-20 minutes to a few hours. Slight warming makes the process quicker. You can safely leave steel in the solution for as long as you wish. Even in a week nothing will happen to it. Some claim that cast iron shouldn't be kept in Evaporast for longer than 12 hours or so to avoid some surface roughening. Also, I've heard anecdotal evidence that springs can become more brittle after prolonged Evaporast exposure. I never had a chance to notice either of those.
Be prepared that some areas (especially those with a bit heavier rust) may develop black spots (converted rust). You can remove most of them by wiping, but some may still remain. Frankly, I don't even bother washing the parts after using those solutions: both of them will provide continuous rust protection for some time. Wiping to get rid of the majority of black spots is more than sufficient, but serves no reasons other than purely cosmetic.
When a part has a heavy rust, you may need to brush it a few times while derusting in phosphoric acid or Evaporust.
Extremely heavy scaly rust is easier to deal with by electrolysis.
