2 questions!

Hello all! My daughter and I have been discussing rat ownership for a while, and have done a bit of research on them. 2 things I want a direct response from a community with experience, first thing is I know we shouldn’t wash rats because of the oils it could strip. However, could I make a little pool for them to swim/dip in for hot summer days? I wanted to make a little summer enclosure so when we were outside they could be too, and I was told they could swim. Is this not encouraged for the same reason? The next question is, I have just learned that they scent mark, and I’m curious does that create an obvious odor over time? Thank you in advance for any responses!