Plastic container... submerge the container into the tank, fill it with the eggs (removing leaves as needed) and move the whole container to the new tank - leaving the eggs to 'float' in the new tank for a while. Personally, I'd probably just let them stay in the container floating in the new tank until about 2 days had passed... Adding meth blue to the container (won't stain the whole tank this way) and complete 50% water changes daily (with an airstone in the container)... by the time the eggs are ready to hatch, the meth blue levels will be way down... Once the fry hatch out, you can release them into the tank.
If you want to grow out 250 fry, you are going to need about a 50 gallon long tank... If you are trying to maximize a single "batch", then you'd want to split them between the two tens, then move some to the 30 and do it a single batch at a time... but even then, 250 is going to be pushing the bounds. Unless you are willing to do twice daily water changes or something...