not sure what to do about the food, but the water..............you can put an ice cube on the top of the water bottle. This will melt and drip down the bottle. The rat will start to drink the drops that come off, conveniently at the ball where it will start drinking from. After a couple of days it will learn that's where the water is and start drinking from it.

I think 3 weeks is in fact too young to be weaned, but maybe one of the rodent people will chime in here and make some smart suggestions.

Judy, Joanna, Jamie.......anyone?