This is often a matter of serious debate. For example, in New York legislators are considered part time, so they are permitted to operate businesses or be employed while in office. This creates an appearance (at a minimum) of conflict of interest in many scenarios. Full time employees of government generally need permission by the appointing authority to do meaningful outside business.

This applies to any government employee. A janitor on government payroll generally needs permission to work for a company that cleans offices at night.

This sounds very interesting and sort of funny. Not really sure how it works on other presidential houses, but still sounds amusing since it will probably require rules and guidelines on what exactly to deduct from the president's paycheck, no? What if the president invites someone over, in a sort-of-unofficial way but not really, do you get deducted as well? or maybe not because it was "for the job" sort of?

Definitely interested to know more.

I read about this in a book called The Residence: Inside the Private World of the White House, which was decently interesting.

Like I said, it does sound reasonable but apparently it does add up. From the link:

"[Laura] Bush wrote that a bill came monthly, itemizing everything she and her family owed, including food, dry cleaning and hourly wages for waiters and cleanup crews at private parties."

"There were some costs that I was not prepared for," Bush wrote. "I was amazed by the sheer number of designer clothes that I was expected to buy, like the women before me, to meet the expectations for a first lady."