My apartment, sadly, does not have a tub.

遗憾的是, 我的公寓没有浴缸。

You should always have a tub of this and get the whole milk stuff not the fat-free.

你应该总是喝一桶这个，买全脂牛奶而不是脱脂的。

For example, say you have a tub of water and two balls of the same size, but of different densities.

例如，假设你有一个水族馆， 两个大小相同但密度不同的球。