What's the easiest way of plotting an undocumented airstrip, found on Google Maps, on SD?

I've looked at Custom Data, but the light hasn't dawned.

Currently I create a Waypoint where I know it is roughly, and via the created SD Waypoint, see where it takes me on Google Maps, and then shift it manually (after 5 or 6 attempts) until it is a best fit.

There has to be a better way?

And related query, if one knows the Lat / Long of the airstrip, what format is accepted in SD?

Thanks.