We are in the process of selling our house. We seem to be somewhat challenged by the buyer who is asking countless questions we were not expecting and / or appear trivial - minor. Their survey report reported that the external inspection chamber showed a minor build up of waste. We challenged this as we have never had any build up of waste or blockage in the 20 years we have owned the house. The only point we can consider is that the drain does have a flow of liquid just enough to wet the underside of the pipe passing through it when the manhole cover of the chamber is raised. I have never considered that this could be what is being classified as minor build up of waste. We are being told by the buyers to have the drains inspected and cleaned. Any view on stance appreciated. Steve.