Feed in tank or feed in separate container are both a-okay. Just like using plastic tub versus glass/wood tank are both a-okay.

But, just be sure you're not doing it out of misguided intentions. For example, feeding in a separate container to lessen the chance of getting bit is a misguided intention. Or not using plastic tub because it is snake-abuse to house a snake in such a small space is a misguided intention...

There are valid reasons for feeding the snake in a separate container. I feed this way. No, not because I don't want my snakes to get cage aggression. The main reason is, I have one of those "naturalistic looking" vivarium with tons of stuff in there and I feed live rat. If you drop the rat in the vivarium, the rat will have tons of places to hide that the snake will not be able to get to. If I hold the rat's tail with tongs, he poops and pees in the vivarium scared and he can break his tail off. I figured this is too much hassle and unnecessarily mean to the rat. So, I decided to feed in a separate container and use that time either to spot clean the viv or do the complete overhaul clean-up since it has become a routine.

There's really nothing much to feeding in a separate container. Pick up the snake, put him in one corner of the feeding tub, put a rat in the other corner, supervise until the rat is securely coiled, then wait or do stuff like clean out the vivarium, until the snake is done eating (no more squeezing movements), then pick up the snake again and put him in the viv with the least movement needed.

I've been doing that since 2008 without a single mishap. I even did that to a mother who was maternally incubating - she went super aggressive on us while she was brooding on the eggs, so we had to use a towel to uncoil her from her eggs to avoid the strike, feed her in the feeding tub, then put her back on the eggs. No problem. We discontinued this though. It started to get really tiresome trying to not get bit when we take her out of the eggs. So, we just did the "hold the rat by the tail" deals and fed her in her viv.

Now, if I was feeding f/t, I probably won't bother with a separate feeding tub. I can always clean out the viv when the kids are playing with the snake.