The pipes between each tub is 3". I don't use a strong pump, it usually takes an hour after I add nutes for the ppm to stabilise. The roots also have heaps of space so I haven't come across the roots clogging the pipes in between the tubs. The piping that leads to the res container is 1", this seems enough so that the pump doesn't drain the res level lower than the rest of the tubs. The return lines are 3/4" pipes, this is where the pressure is highest so going thick pipes isn't necessary. I aimed to make the system as even as I could. Ideally the system would be better if the intake and return lines lead to the tubs directly but I was short on space hence the design I went with. I kinda went by trial and error and so far this is the best design I've come up with. The next idea I'm thinking of going is reducing the height but creating a full 8 foot x 4 foot bed and ditching majority of the plumbing. Not sure what you would call that system, still circulating but in one pot.@Mospeada What are your pipe diameters? I think I see many people using 1'' or even 1.5'' for pump-out-containers-in pipes and 3/4'' for containers-out-pump-in. I was thinking having everything 3/4'' but I just don't know. I am not a plumber and I have a hard time finding a good general resource on the net for deciding suitable pipes for arbitrary water installation safe for this one (here) which must be overkill compared to just some good experience based heuristics. Oh by the way I have my three danner 700 GPH coming in soon. They come with 1/2'' FPT pump-in and 1/2'' MPT pump-out which I find a bit small for any application of that capacity.
PS I was also thinking to maybe use flexibel pipes or even hoses for the connections including valves. For easy maintenance of containers or slightly rearranging the floor plan of the containers.