Step one buy 1 unit of population from gremak pirates to access slave collars
step 2 research slave collars and militia
step 3 after invading a world deploy enough forces to enslave the entire population (both rebels and not) Be certain to have extra empty transports in the assault force, I prefer to have a quantity of my preferred population type to reseed taken/stripped worlds.
step 4 free the slaves, load all the now content population into troopships.
I find this a good way of padding forces and holding worlds.
Note that this works best for races that you do not want to have in your empire ( I use it on the gremak primarily) because others of that races elsewhere in your empire will take issue with it.
Tinkers do not need food, and ignore morale. They are always content, even if newly captured.
Designate a single large desert / arid / hive world for your captured tinkers (ideally use a whole system if possible). Remove all other population except androids (who also have no morale). As you capture tinkers ship them to the tinker megaworld. Build it with only factories, and keep filling with tinkers. If there are other worlds in the system seed them with tinkers as well, and use them to fill the primary world as their population grows. Use the primary world as your main shipyard. Since there is no population cap you can easily get it to a population able to support all the factories at maximum capacity and produce even the largest of hulls quickly.