You may store the markers somewhere (e.g. in a object) and use the latLng as key:
var markers = {};
/*......*/
markers[myLatlng] = new google.maps.Marker({
position: myLatlng,
map: map,
title: 'Hello World!'
});
/*.......*/
function removeMarker(lat, long) {
try {
markers[new google.maps.LatLng(lat, long)].setMap(null);
} catch (e) {}
}