Parse HTML source code from variable and not website.... using DOM.

I have successfully been able to parse HTML from a website:
TestParser parser = new TestParser("http://www.domain.com");
List<Pairing> pairings = parser.ParsePairings();

DBSave.SavePairings(pairings, userID);
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This works.
Now I have to submit a form via C# code.... DONE.  It works.  And my C# code saves the "new" HTML to a string variable called "submitParsedHTML".


My question is: how to I change out the URL, to go through the string variable instead?
I am thinking about doing this:
When the user clicks the button to "Post" to the form and the app grabs the HTML.  The app logs into my FTP account and saves the HTML as a seperate (temporary) file to be used on the internet (ie: http://www.mywebsite.com/temp/userID_testwebsite160810.html).  Then the app can then parse the HTML as if it was a normal HTML document and not have to go throug ...