I thought I'd ask before I need it rather than wait for an overflowing
sink.

Moved house. New unbranded bathroom suite came with the house. Wash
basin has a push-to-close-push-to-open waste plug. I've never had one
of them before and there's no obvious way to take the plug right out
for cleaning. Rotating it doesn't seem to raise or lower it so I guess
it doesn't unscrew and nothing budges when I pull gently. I'm loathe
to pull hard in case I break it when there's nothing (yet) wrong with
it.

How do these things normally work?

Any suggestions?

Nick