Inserting form var into Where clause in DbMultiRecLoader

I have a form using DbMultiRecLoader, and it has a variable passed from another form which I want to use as a selection criterion in the Where clause on the Advanced tab. The variable is in $form->data[srch_name], and if its value is SMITH, I want the Where clause to read 'mast_name = "SMITH"'. How can I get the variable value into the Where clause? I have tried using the variable name enclosed in php tags, but the resulting query has WHERE mast_name = "".

Found the answer - the php code was missing "echo"