plumbing, soil stack, fosse issues - please help!

[amanda]

Sorry this is so longwinded but feel i need to explain as fully as poss. We are trying to install an ensuite in our grenier and have got to the stage of plumbing in the shower, sink and loo. We have a fosse septique, old style with separate entries for grey waste and toilet waste. In our cave we have two large pipes which were used for a bathroom that was there before and we are hoping to use one of them and have therefore tried to trace them to the fosse. One of them seems to go nowhere, ie. if we put water down we dont see anything in the inspection chamber (after the fosse) the other one seems to take grey waste. My question is, is it possible to put grey waste into the fosse directly with toilet waste or does it have to be separate, and also if we just use the toilet for liquids (no number 2's or paper) could we connect the toilet to the grey waste pipe that bypasses the fosse. Also does anyone know if there is any reason why we cannot put the soil pipe on the outside of the wall. Thanks for any replies.