HOW CAN I STOP MY PLUG FROM LEAKING?

MY SINK HAS THE NEW TYPE OF CHROME STRAINER PLUG WHICH IS A PUSH IN TYPE. IT HAS A BALL HALFWAY DOWN SHAFT AND A USES A BLACK TYPE OF WASHER UNDER THE CUP. IT IS NOT OLD BUT HAS ALWAYS LEAKED SLOWLY. IHAVE REPLACED IT AT FOCUS WHERE I BOUGHT IT COMPLETE WITH THE WHITE CERAMIC SINK BUT THE REPLACEMENT ALSO LEAKS SLOWLY. CAN I CHANGE TO A NORMAL TYPE AS I DO NOT WANT OR NEED THE STRAINER?