I don't mix business with pleasure. Is the correct idiom you are looking for. For your circumstances. "Don't s•it on your own doorstep" = another idiom used by thieves, gangsters and delinquent teenagers. it means they do not commit crimes in their own neighboor/neighbourhood. in an attempt not to be recognised by the local police or the local community. You are mixing up your idioms. "I don't s*it where I eat" is a modern version, to mean what you say, but it was taken from the same older Idiom "Don't s*it on your own doorstep" or the idiom "I don't mix business with pleasure" so it is just a change in meaning. from a few generations ago to today. There has been some bad attempts by people to update older idioms and they do not always work. it is mixing up the original meanings with a new hygiene meaning that spoils the idiom. THE URBAN DICTIONARY is not a very reliable source for all idioms, I can go there now and make up a stupid one.

"I don't date co-workers." is the polite way to say it. Another vulgar way to say it, for men is "I don't dip my pen in company ink." But it's not a professional thing to say. If you did say that at work, many people would think that you were very, very rude.