So the tank its on its way to be welded and sealed after the most laborious wash and cleaning I've done to a tank. 5 washes actually.
I cleaned and reconditioned the inner filter of the suction structure, leaving not even a speck of dirt.
The first picture speaks by itself. It was rusty mud in there. The inner filter's metal screen was clogged with super small particles.
I have a busy week coming along!