Walesreno

Hello all, recently bought a house to renovate. it’s a stone built terrace c.1900 with a single storey Brick & block extension c.1970 ive added some photos and attempted to edit them on my phone to illustrate what I am trying to achieve. at the moment , the ground floor extension contains a bathroom. the toilet waste goes straight down into the slab & then under the wall, and follows the “alleyway” down into the inspection chamber. the basin and toilet are fed into a gully trap then that flows on a separate line, into the chamber. So as to say. There are two separate 110mm pipes entering the chamber from the bathroom wastes. We are installing a wet room in the area the bathroom was. To do so means widening the room and digging up the existing drainage to replace. i propose a stack be fitted as in my photo this would allow for the new wall hung toilet to go horizontally through the wall and then into the stack on the outside of the extension as would the basin the shower however - I’ve estimated would be exiting the building about 70mm below DPC level and probably within the concrete path level outside. and that is my issue. Can I and if so how connect the shower waste to the stack like a propse ( red line ) below ground level. and does my proposal overall appear to be suitable/doable? if anyone would like further info just let me know. i look forward to hearing all of your advice 👍🏻 cheers all!