Creating New Inspection Chamber to Access Another Junction for Rodding

Hi, I have built a kitchen extension over an inspection chamber taking waste only from my kitchen and upstairs bathroom. The inspection chamber allows access to the point where the two pipes (kitchen and bathroom) drain into a bigger, main pipe which runs out of the extension. I would like to tile over the existing chamber (thus rendering it invisible although it will remain technically accessible if we break the tiles, i.e. it has been raised to scree level and has a double seal) and create a new inspection chamber over the main pipe, just outside of the extension. The objective would be to create a new rodding point down the big, main pipe because I want to cover over the one inside the extension. My question is whether this new, outside inspection chamber would offer sufficient access to rod the old junction point. It's only a few feet further on so quite close, but the question is how they would rod a junction point where there are two different pipes that the rod could go through when it gets to the junction? If the blockage is in the bathroom pipe, how to get the rod to go up that one and not the clear kitchen pipe? Do they have tools that can differentiate pipes? Thanks.