I have a metal building and my walls are thin. However it is installed and sheet rocked. This is what we call are game room and all my plumbing is on the inside walls covered with foam tubing I have been told sence my water lines or on the inside I can not put a 90 degree angle into the wall and a 90 into the box? Is this true will it slow down my presure.
There is no problem with multiple 90 degree elbows. Yes there will be some friction loss due to the elbows, slightly affecting your flow rate; no it will not make any difference, your washing machine may take a few extra seconds to fill up is all. Describing the situation exactly will help you get the best answer.