Outlet for wc flush overflow

[RrogerD]

Can you plumb the 22mm overflow from the cistern back down into wc outlet?
I have, or rather will have, a 38mm pipe running from the adjacent basin into the wc outlet and plan to tap into this rather than coring a hole through the porcelain tile and the wall behind.
I know there is a possibility of smells but in reality, how likely? The S&V pipe is just the other side of the wall and has it's vent to the sky, just a couple of metres above this.
Thanks

 

[RayCaister]

Internal overflow .....https://www.plumbingworld.co.uk/fluidmaster-pro550uk-duel-flush-valve

 

[Madrab]

I know there is a possibility of smells but in reality, how likely

Let see - it's the main outlet to the soil pipe and for the toilet, where smells would most likely be found ...

As suggested, a flush valve with an internal overflow would probably be the best option

 

[RrogerD]

Internal overflow .....https://www.plumbingworld.co.uk/fluidmaster-pro550uk-duel-flush-valve

Thanks. Had a quick look. Can't work out how it works. Will I be able to fit this to an older, lever-handle cistern? Where does the overflow water go?

 

[Madrab]

The overflow water runs into the tube on the side and runs into the pan,

If you have a manual syphon dual flush valve then you can get replacements with an internal overflow too. if the toilet is close coupled then you will need a new doughnut sepcific for your toilet type too if the flaush valve is to be replaced

https://www.screwfix.com/p/viva-skylo-3-part-dual-flush-siphon-215mm/284hr