[jQuery] super easy jquery question

After I have processed a user request from a form submittal, I want to
remove the text from a text <input> field. With JQuery, how do I do
that? The input field has the id of #subject.

I've tried the following, but to no avail. (I clearly don't
understand jquery). Please help.

$('#subject').val()="";
$("#subject").text('');
$("#subject").text().replace("");