Help please. Tank fitting required

[Eggle]

I have 3 old 200l drums and wish to connect them together. I want to do this without cutting them up, so my idea is to drill the hole and feet the connector into and through the hole using cable / hose. Then I need to screw it tight.
What i need is something with the flange on the inside and the thread through to the other side so I can then hold the connector and tighten the nut, with out the need to get inside the tank.
Any ideas on where to find the fitting.

[Mexico.]

Flange sorry i can't help

[Pigeon]

Plumbing shop, fittings for connecting pipes to water tanks.