[Slick]

My small transports can carry 450M; that's using a MC, engines, QR and solar sail with the rest of the space taken up by Cargo Bay III's. Occasionally the transports do need to dump excesss population, but this can usually be coordinated easily enough. There's always the option to jettison them to make room, but I usually don't do that.

In a normal game I routinely have transports which carry 3-4 different breathing populations, once I get them. By (D)ropping all population at the destination, each different species will multiply on the planet at the end of the turn, thus ensuring that there is always >1M of each kind on the planet (unless the planet gets filled). Then I load all non-breathers onto the transport, which undomes the planet, give the planet whatever orders desired and order the transport to (D)rop the population at the next planet. Rinse, repeat. Occasionally the transports are redirected to a different planet to offload accumulated species of one kind or another. Works like a champ. One thing I do to make this more efficient is that if I am colonizing a non-breathing planet, I just put 1M pop on the colonizer. This minimizes the excess population at the point of undoming. Another thing I do is keep a transport with all the different species over the planets where I am building colonizers. This way I can load the correct population onto the colonizer before giving it orders to colonize. This creates an undomed colony from the start. Another option is to first send the colonizer to a planet with the correct population then give it the order to colonize the target planet. Kinda the same outcome using that method.

I also use a few transports to keep my largest native-breathing planets from being wasted because they can't make more population once they are full. When they get full, I'll offload some and dump them at outlying native-breathing planets. This keeps my populations all growing at the max rate.

edit: *sigh* if only the Transport Minister would work this way...