Focusing on one Manufacturer while still computing the correct totals means that we need to assure that the query still pulls all 5 manufacturers. Unfortunately filters strip off all other manufacturers from the query and Tableau becomes unaware of what the accurate total should be. Instead use the "Hide" function - this retains other manufacturers but simply does not display them. This allows us to compute the correct % of total.
If a quick filter control is desired, you can also use table calculations to force the filter to only hide information. to d so create a calculated filed with the following formula:
When you add this field to the level of detail and generate the quick filter off of that, it will create a control that will only hide members rather than filter it out.
Hope this helps!
Wilson is correct. This thread contains the same advice: http://community.tableau.com/thread/119973 but we discovered a limitation to this technique where it only works for the one worksheet, not the entire dashboard, which may or may not be an issue for you.