The message .com
from "marc_ely" contains these words:

It's a modern close coupled type with twin button push flush. The
valve assembly is a weird looking thing (at least to me). There's no
overflow outlet - so I presume it has an internal (to the bowl)
overflow.

If the core of the lifting wossname is hollow then that's where it
overflows. I'd fit the filter - there's not particular reason why not
and it'll just possibly catch some bit of crud and save you a dodgy
valve.

If it's mains fed, it may well have also come with a flow-reducer of
some sort. Without it you'll get a very concussive shut off.

--
Skipweasel
Pay no attention to that man behind the curtain.