Rose wasn't the only one to be privy to this, however. In fact, once Donna boarded the TARDIS, one very inconvenient thing ceased to exist. Mainly, his shyness. Thankfully.
Donna was listening to the PR woman advertise the purchase of one of the weird octopus-head creatures for servitude. She tried not to think of the human rights implications, as it was the future, and the Ood were aliens. Instead, her attention centered on the Doctor. He seemed to be thinking, then was stretching his head up to look around for something.
"What are you looking for?" she asked.
"Sign to the loo," answered the Doctor plainly, slightly worried at the fact he couldn't see any.
"What's wrong with the TARDIS?"
"Too far away, I'd need to bring my psychic paper to be let back in, and while I'm gone, you might do something to arise suspicion. No psychic paper, no credentials,"
"Check the map of the complex," Donna suggested. Sure enough, there were several.
"Brilliant! Right down the hall. Back in two ticks!" he said, walking out of the room.
The Doctor was even more pleased to find a single stall toilet.
When he came back, Donna had become curious of something.
"Why didn't you go before we left? And 'I didn't need to' is not a reason,"
"Well, for me that's a pretty good reason actually. As a Time Lord, I've got a pretty big bladder. If I don't feel anything, it usually means I'll be fine for a while. At least, usually," answered the Doctor.
"So, not this time?"
"No."
Donna got a sudden thought. "So, how often do you need to go?" she asked.
"Every 2-3 days, depending on fluid intake," he stated, making Donna more suspicious.
"When we were at Adipose Industries, did you hide in the gents?"
"No, broom closet."
"So.. hold on. We were in Pompeii for two days. Repeat of my first question," Donna asked.
"Forgot in all the excitement. Really good at refocusing. Probably shouldn't though," he conceded.
"No, you shouldn't," Donna agreed.