[plumb4u2]

I appreciate your input dyount but there is no way this house has a whole house trap

I have been in the service biz for 17y and have worked in many houses over 100y old and have NEVER seen a whole house trap

without a response from the OP I can guarantee this house has cast iron main stacks with galvanized steal branch lines to the sinks (very common in 30's)

any gurgling he is hearing is because the galvanized lines are rusting shut