hose size doesnt matter. the outlet pipe assembly has a little plastic ball inside which is a safety feature. if the shower overheats the water,the ball can drop down and shut off the water to the hose assembly and cause the water to backflow out of the overflow port.
andabate
November 2011
Apparently you cannot use any replacement hose otherwise water will pour out of the little spout at the back - makes you buy from them!!