Relocating mobile home pluming?

im thing about buy a 33 year old mobile home, it has 3 bedrooms and is not a double wide.master bedroom is ok in size butt the other two aren't.was thinking on creating an open floor plan bye tarring down some walls including the old bathroom and turning one of the other smaller bedroom into a new bathroom...what should i be concerned with when relocating sewerage ? do i need a certain pitch?a new vent stack ?the new bathroom will be on the other side of the wall where the kitchen is located now...