What I am trying to do: I have 2 drop-down fields on my form. They each ultimately go into the same field in the database, but contain different lists, depending on whether they are a department or an external customer. Using PHP on the next page, I have it set to accept the first field entered (with a back button to go change it). A couple of people testing it requested either 1) a button to clear the contents of a field with a button, instead of having to scroll up to the null value, or 2) when you select a second item, the first is automatically cleared out.

Is there a way with javascript to accomplish this? I found this code while searching online, but I'm not sure how to attach it to a button on my form:
document.getElementById('numquest').value=null;
I am assuming in this example that 'numquest' is the field name to clear.

Thanks in advance for any assist!

Trish