Gastank rinsing and cleaning using a concrete mixer

Today I have been rinsing the tank using a concrete mixer. In the morning I went to the DIY market and bought a few cans of cleaning vinegar, parker screws, ducttape  and hammerite paint. I drove to my brother in law who has a mobile concrete mixer which I could use. With two tension straps we connected the tank to it and presto!

First thing I did was rinsing it out with water:

And a lot of brownish water and rust particles came out, this picture was taken after the 2nd rinse:

I think I rinsed it about 4 times before clean water came out of it. Then I put 15 liters of Vinegar in it and about 200 large parker screws. Not sure if this was a clever thing since the inner tank had various inner plates - likely to absorb gas movements. Then using duct tape to cover off all holes. I had it running for about 20 min and released the content which was again very brownish water. Then I rinsed it again a few times with water until it was clean. The screws however didn't came out, sigh! So I took the gastank back home again and used a flexible magnet stick and eventually got them all out. It was like playing "dr shiver". Glad I bought a new box of large screws rather then throwing in old small nuts and bolts or small stones. It's now drying up again and tomorrow I will paint the surface rust spots with Hammerite.