The Prophet used to go round to all his wives with one bath.  

أَنَّ النَّبِيَّ ﷺ كَانَ يَطُوفُ عَلَى نِسَائِهِ فِي غُسْلٍ وَاحِدٍ  

"I put out water for the Messenger of Allah for a bath, and he had a bath after going to all of his wives in one night."  

وَضَعْتُ لِرَسُولِ اللَّهِ ﷺ غُسْلاً فَاغْتَسَلَ مِنْ جَمِيعِ نِسَائِهِ فِي لَيْلَةٍ