Don't you are heading for serious trouble if you do with leaks of WC waste and all other waste and it's illegal to connect to the drain direct it has to go via an existing open gulley or back sealed drain at surface level from there it discharges into a manhole set in the main drain. It will be discovered by a surveyour when you sell the property. Ignore this at your peril if you go ahead you may find it will be condemed and you will be forced to have a proper repair carried out at considerable cost or even the whole drain run replaced from manhole to manhole. Contact your local authority planing office aske to see a surveyour [there may be a charge] tell him/her you 'Value their advice on this as it will save a costly mistake'
I've not done jobs like this but guessing the surveyours may suggest a 'lift pump' similar I think to a WC macerator pump.
To put it bluntly the macerator mashes the solids from a WC to enable it to discharge liquid form through smaller pipes that normaly use for sewage like your main drain size of 4 or 6 inch. It's cheaper to get expert advice from the surveyours than make an extreamly costly mistake.
Good luck
Bob retired builder of many manholes
