I know this is probably common but we have a real problem when our boys go to their dads (every other weekend). I am stepdad to 3 lovely children, whose dad doesn't make any effort at all towards the personal hygiene of the children.
He will be picking them up in 10 minutes and will have them til 6 on Sunday night. In that time they will not have a bath, shower, wash of any sort and will not be asked / told to clean their teeth once either.
I know his and DW's marriage ended badly, but I find it utterly despicable that he uses them like this to score points - as he knows how much it upsets / disgusts us.
We also do our best to send clean clothes for the weekend, as we know he refuses to wash any clothes for them (because 'you got custody' apparently!) - but he doesn't tell them to get changed either (boys are 8 and 11 and being boys do often need telling!).
I know there is nothing we can do to make him look after them better, but it is just so frustrating. And when they visit their paternal grandparents (Sunday afternoon) they will be smelly boys in dirty clothes which makes it look like we can't look after them properly.