Simply Koi and More Koi

Can anyone advice me on this, I have been given 6 ibc tanks 1000lt and I want to connect 3 of them together in my shed for growing/ quarantine tanks I was thinking of gravity fed to each one then a pump in the last one to a filter then back to the first tank . What size pipe would I need. I've seen a few different ways on google but don't know the size pipe so they don't overflow. I was thinking of a 2" pipe at the top flowing into the 2nd tank and then another 2" pipe into the 3rd tank and from there a pump into the filter then back to the 1st tank. Would this work. They all have bottom drains so I can clean them well when I need to

I would suggest a paralel arrangement instead of a serial setup. This would avoid concentrating waste in the down stream tanks. I think a pump rate of about 8000 l/hr would be about right

B. Scott