open sewer in your garden dangerous fumes in there not to mention smell and rats
always told trap and vent if there ain’t a vent in line plus it ain’t alway concrete up what you’ve put in you need it for blockages if you ain’t got any rodding eyes then leave a manhole cover
when you tap in normally i’d make a circle hole by stihl sawing a load a slits then knock them out fit a collar so there’s no way out is protruding inside the existing because out is you’ll get blockages
we’re you have circled and the other one just wants 2 pea traps setting in there 30 bar proper job