Cistern/Convert from internal to external overflow

[Nitell]

Hello guys.

My Dual Flush Torbeck Opella cistern has an internal overflow. It is now necessary to change the bottom entry inlet valve.

Neighbours sometimes cause blockage in the drainage/manhole.

I now consider to convert the cistern to overflow externally.

How could I block off the internal overflow?. With a rubber bung of some sort?.

The photo show the hole is not totally round. Any ideas, please?

 

[Nozzle]

Just set the external overflow at a lower point

Nozzle

 

[terryplumb]

The overflow on your flush valve looks as though it can be adjusted ,if so raise
It higher ,and set your external accordingly lower.

 

[Nitell]

Yes. The overflow can be raised. Thank you. So I will do the conversion.