Overheating during idle

I have not driven it.
T
he water was solid rust color when I flushed it. I used a flush kit so I was putting water into the water pump/intake ports. I ran it, let it cool down, drained the radiator then repeated until the water came out clear. Thought it would not hurt to have the radiator hot tanked to be sure it is flowing well.

Water pump had some corrosion.

What do you suggest to figure out if it needs a new gas tank or just cleaned? Do I have to drop it or just pull the sending unit to inspect and remove old gas?

Thanks for all you help