Water softener drain

[SuperPav]

Looking for a bit of practical advice...

 

When we did our understairs cupboard (where all the plumbing manifolds and water main etc. are) we put in a 28mm pipe to the outside of the house for a D2 discharge pipe. Things have changed and the UVC is now going elsewhere, so we sitll have the 28mm pipe.

 

I want to put a water softener (one of the twintec things), so assumed I can just use the 28mm pipe for the discharge. However, having got the unit, it says I need two separate drains for a discharge, and an overflow..

 

Given the only location to put it is in this ground floor cupboard which is the middle of the house and there is no soil/waste pipe other than the 28mm one, am I completely snookered, or can I put both of them into the 28mm pipe either directly or indirectly with separation etc.? Really want some soft water