How do I not let this control my every thought?

[Travis]

how have you all dealt with disciplining the children during the separation? the reason i ask is because tonight I picked my boys up and we weren't 10 minutes down the road tonight and my youngest, almost 4, says "sh#t". I asked him what he said and he immediately started crying, knowing he was wrong.
Now, I was brought up in a strict household, not beatings, but I got whipped with a belt. I don't remember the last time I whipped my boys, never with a belt. My WAW grew up in a house with very little discipline. It's always been a bit of an issue with us.
Anyway, I told my son when we got home he was getting his mouth washed out with soap. When my oldest was 5, he cussed and my wife washed his mouth out with soap. Not actually washed it out, but made him sit there with a bar of soap in it for, like, 3 minutes. That's what I was planning to do. We are getting ready to go through a custody battle (if you read my earlier posts you will see why)so I call my WAW and told her what I was going to do and she said no way. My attorney just filed temporary custody papers, which she hasn't got yet, so I didn't want to get into a disciplinary issue.
I asked her why it was okay for her to do it to the oldest when he was 5, but I am not to do it to our youngest. He's always been the baby and her discipline has gotten even more scarce since "the bomb". She said no way was I doing that. I've been doing a good job of detaching this week and didn't want an argument now so I told her I wouldn't.
I feel like this is just another case of her wanting control. Some of you may not agree with my form of punishment, but it was okay with her before, but not now.
Opinions, please.