Keep reserve Diesel tank or Toss it?

[JordaanDMC-12]

I'm doing a extreme makover today on the 220 hence my previous post about the turn signal, basically i'm trying to fix most of the small issues it has that don't require major work.

I ran into weather I should keep my spare tank or toss it. The past owner lived in Mecca, California. Mecca doesn't have anything in it let alone back in 1970. I imagine he had this looks to be about 12-13 gallon spare tank put in because Diesel stations weren't a abundant as they are now.

Well I pulled it out when I first got the car and it's been sitting on the side of our house ever since. After talking to Charlie about it at the So Cal GTG a few days ago I decided to clean it up an reinstall it. The problem is there is no way to take it apart to clean it. It's welded together and the only holes are to put to Diesel in and to let it out.

I bought some Diesel and ran it through and all these little flakes came out and other crud. I then ran water through it non stop and checked the water coming out every now and then and it looked clear. I went and bought more Diesel and ran some more through but i'm still getting little flakes and all this other crud. I don't know if I should just keep trying to clean it and get diesel after diesel running it through or if I should just toss it.

It's rusting on the outside on the bottom so I don't know if it's rusting on the inside either. I don't really know what to do. It'd be awesome to keep it and have a spare tank, but if there is no way to get rid of all th crud in there except have it run through my engine then I think I may just toss it. I don't know what to do though :S

I think it's made out of steel too. I think.