Where is it brought down that one should wait after going to the bathroom and before having relations. I have heard this before and 2 reasons given. One is that because of the "ruach rah" in the bathroom that (I guess?) "attaches" itself to the private parts of ones body and therefore should avoid relations until a certain amount of time has past (next question.) And the other reason is because some sort of danger if the urine mixes together with semen. What are the sources for both reasons (if the 2nd one which I only heard once is valid.)
As well how much time is it that one should wait?
And is the only problem the "actual" relations or even the time the couple will spend together before hand.