Rust in coolant system?
 

Took a look under the radiator cap for the 1993 Honda Accord and noticed what appears to be rust inside. The coolant reservoir on the passengers side to the left of the radiator cap also has rusty colored liquid inside which has left rust colored stains on the black tubing that goes through the reservoir cap.

1. I would assume it's rust but it appears the reservoir is solitary so the presence of rust inside wouldn't make sense since it's all plastic. Unless I'm wrong I assume the system sucks coolant out of the reservoir and propels it into the radiator without allowing the reverse to occur. Would this conclusively rule out rust and instead this must be some rust colored coolant?

2. The level of fluid inside the reservoir is below minimum.

3. I'm not sure what it's supposed to look like under the radiator cap but it's wet with rust colored gunk and there's no coolant visible. I would say dry as in there's no visible coolant but it's still caked in rust colored gunk so it's not technically dry.

4. At this point I don't know what kind of fluid the previous owner put into the system. I'm thinking about doing a total flush and then refilling it. Is it plausible? Or am I just insane? I'm looking for an easy way to flush the coolant system but the videos I've watched appear to be vehicle specific. I can use a garden hose if necessary?

5. What kind of coolant? Honda only or any no silicates no borates like the green stuff from Prestone?

3. Do I pour this stuff into the reservoir or the radiator?

I'll hit a few.

1) yes the reverse does happen.

4) Yes, you are low on coolant (? Which could be a concern-leak). You might top it off with water first. Run the car for a while and check for leaks, and or rent a pressure tester and verify no leaks (should hold ~15psi)...any leaks, fix/replace/repair the source. Then do the flush.

5) not wanting to start a debate....once flushed you can use non-Honda coolant...no worries of mixing at that point.

6) refill the rad/engine with the proper mix (50/50...unless you are in a VERY cold area). Be sure to follow the procedures-heat on max, use the bleeder, ect- to make sure all air is out of the system. Fill the reservoir with 100% coolant.