Assuming your page is built using classic the ASP API 

//Example to show how to build a clear button on a new entity search screen
var strSearchFormClearButton = CRM.Button("Clear", "clear.gif", "javascript:document.EntryForm.em.value='6';document.EntryForm.submit();");
myBlock.AddButton(strSearchFormClearButton);

Assuming your page is built using classic the ASP API 

//Example to show how to build a clear button on a new entity search screen
var strSearchFormClearButton = CRM.Button("Clear", "clear.gif", "javascript:document.EntryForm.em.value='6';document.EntryForm.submit();");
myBlock.AddButton(strSearchFormClearButton);

I used this guide as a template: https://www.sagecity.com/sage-global-solutions/sage-crm/b/sage-crm-hints-tips-and-tricks/posts/creating-a-codeless-search-screen-on-an-external-database-using-runblock

OK.

The Codeless approach may take you so far but you may then find you need to create the page in code.

That is a little above my skill set at the moment, but good to know. Thank you for your input!