Webforms PHP Help

I am trying to use php to delete a webform submission. This seems like it should be soooo simple, but for some reason I am getting really confused reading the docs and looking at the functions.

Let's just say I want to delete sid#123 from node#456. $node, etc isn't really helpful because I want it to occur from a different context than the current node anyway.

I am sure it will be so simple!

Thanks for your help.