I think that your problem may arise from what you originally said,
our flight home is on 2 different airlines and we don't think we will have enough time to get our lugage, get through customs, check the bag on the next airline in time.
I can't see how one bottle would make a difference in that. It sounds like you have a tight connection. Except if this is on two different tickets the second airline won't wait - or take care of you - if there is a delay or problem with the first flight.
If you had to retrieve the luggage from the first plane and re-check it on the second surely the one bottle wouldn't make a difference. You declare it, it is under the limit, you move on.
If you were 100% carry-on, that's where the problem could be.
But it sounds like your connection is too tight to me.