I can't help you with your main questions; however....
It's still not quite 250 ml, but check out this 120-format developing tank. I've got a couple of these and they use 260 ml of solution (the figure is stamped on the lid, and you can sort of make it out in the auction's photo); however, they can't use inversion agitation, just rotational agitation via a rotating stick. I find this very difficult to get right, so negatives developed this way often have streaks. If you're used to this type of agitation and want to save a little money on chemicals, one of these tanks might be just the thing. I believe that Jobo-style rotary tanks could also do a roll of 120 in a similar amount of solution, but I don't know the exact figures offhand. I've seen posts from people who use Paterson-style tanks in this way (rolling them on a countertop) to save chemicals, but I've never tried that.
Hey, I have one of those tanks although I never used it. I have used newer (than that one) tanks with rotation, such as the Ansco, and never had streaks.
I would guess maybe you need to rotate a bit more vigorous and alternate directions. If that doesn't help, maybe its due to the low volume?