I replaced all our waste pipes with smooth plastic hose from an aquatic shop. The ribbed pipes held the debbris in them and caused a foul smell in the van. We even use the same pipe to go to the waste master. The sink drains much easier now and the smell's have gone. While I acn see the manufacturer could save cost's in the pipe and the installation, the smoothe pipe is mor eenvironmentally friendly to us the user. (no nasty niffs).