how do you tell when they're preggers?

[Moofins07]

The easiest way to tell male from female is to pick em up by the tail and far apart holes = males close together = female. The males testicles are very visible when they are adults (even subadults)

Does the same sexing method apply to domestic rats? I've been preparing myself to get a male and female rat (only the 1.1 group cuz, well, I only have one snake to feed at the moment. ) because I'm convinced they stink less than those darned little mice, and my female's getting bigger, so, I'd rather feed her ONE large item rather than several smaller items.