I needs new valves for my dual flush, close

there is a rubber valve or washer to replace

what happens if you try to tighten the thread more

cisterns never completely empty as the setting of the mechanism to close the valve is activated when it gets heavier than the water supporting it
try allowing more water into the cistern on a fill by adjusting the water level control
get a plumber in to clean out the sewerage pipes as there appears to be an obstruction in the line

You will need to replace the seal under the flush valve, need to dismantle cistern mechanism.

That would be a leaking flapper valve. They are inexpensive and easy to install. Good luck

I’m happy to help further over the phone at https://www.6ya.com/expert/robert_24775b73ca70da93

Perhaps it is taking a long time to fill the cistern, take top off and see if it's filling after flushing, if it's slow and pressure is ok it is likely to need a new diaphragm in the filling valve.

The flapper valve(ball)seat is not sealing. Needs a new seat and flapperat bottom of tank. -Ned-

well, yes... but apart from providing you with a forum in which to vent your frustration I'm not sure how you think we might help. I have the same problem with a dual flush cistern, but in my case I know that the root of the problem lies in the fact that the soil pipe leading from the bowl has insufficient fall (because the previous owner of my house moved the toilet further from the down pipe). Maybe something like this is contributing to your problem too?

There are some dual flush cisterns where you have to depress one button to reveal a cavity in the second button. Put a screwdriver in that cavity to lever out the second button, then release the first button and prise that out.

Underneath the buttons is a screw which must be unscrewed to release the cistern lid.

Not sure if this will apply to you... but if not, good luck anyway.

i presume with lid of u can flush toilet by pusshing switch with finger if so buttons must be spot on when replacing lid can be adjusted inside systern any probs get back