So I've got a prochem legend xl with a dodgy thermo relief valve. I was thinking of plugging the inlet on the waste tank for hot water dump/bypass and then installing a replacement inlet of the water box. This way instead of that pesky thermo valve pissing away water needlessly, any overly hot water can join the freshwater tank and average out the temp. I also would most times have freshwater coming in that's cold. What's the downside? Why hasn't it been designed that way to start?