Apart from the feed both lines i.e. Fill and vent were dully plugged. The most brilliantly idiotic thing I was doing was that while filling up the tank, I used to unplug the vent line and then dully plug it back

Well that is crazy. I guess its too easy to overlook what we tend to consider "non issues". Now i'm amazed that engine even ran for a minute, were the walls of the tank giving in or was it the walls of the tubes...