how can i prevent searchview from having custom title and tag appear in a toolbar?

I think you have 2 options,

Set width to SearchView in styles

<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.AppCompat.Light.NoActionBar">
    <!-- Customize your theme here. -->
    <item name="colorPrimary">@color/colorPrimary</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorAccent">@color/colorAccent</item>
    <item name="searchViewStyle">@style/MySearchViewStyle</item>
</style>

<style name="MySearchViewStyle" parent="Widget.AppCompat.SearchView">
    <item name="android:maxWidth">140dp</item>
</style>

Second option is get SeachView instance in onCreateOptionsMenu and calculate width of your toolbar_title layout set remaining width to search bar.

@Override
public boolean onCreateOptionsMenu(Menu menu)
{
   getMenuInflater().inflate(R.menu.menu, menu);
   MenuItem searchItem = menu.findItem(R.id.action_search);
   SearchView searchView = (SearchView) MenuItemCompat.getActionView(searchItem);
   searchView.setMaxWidth(calculatedWidth);
   return super.onCreateOptionsMenu(menu);
}

But as per android standards, Search View has to extend completely in toolbar. For this we have to use searchView.setMaxWidth(Integer.MAX_VALUE);.