ثُمَّ يُضْجَعُ عَلَى شِقِّهِ الْأَيْسَرِ، فَيُغْسَلُ بِالْمَاءِ وَالسِّدْرِ، حَتَّى يُرَى أَنَّ الْمَاءَ قَدْ وَصَلَ إِلَى مَا يَلِي التَّخْتَ مِنْهُ
Translation: Lay the deceased on the left side and wash with water and sidr until it is apparent that water has reached the portion adjacent to the platform.
The body is on its left side, exposing more of the right side to water. The phrase ma yali al-takht refers to the areas touching the washing platform. Turning the body ensures those areas are washed too.