Waste pipe conjunction

I regret not doing a before and after shot.

I can only think the gully grate originally had built up concrete sides (which would have contained and stopped the waste water running all over the garden).
When the broken drain was discovered my firm employed a contractor to fix the drain, this they did, but just butted the gully up to the old waste pipes (perhaps altering the waste pipes wasn't included in their price).

The custard then complains, hence, I get the job of trying to do something with it.

I did try a few different arrangements before settling on the idea of cutting a hole in the back inlet and diverting all the wastes into it.
The only waste discharging onto the grate now is the condense from the combi' boiler which only drips slightly anyway.

As tom says every day's a school day.

I've often teed wastes in before but never 3 in combination outside into a gully before.