under upset conditions when there is no flow through the annular vent passage fig4 b illustrates the installation of the vent exhaust fan at a significantly higher elevation not to scale than the other components without a vent exhaust fan upstream isolation valve or a branch line isolation throttle valve but with the bypass branch line according to another embodiment of the present invention the utility box 403 is illustrated in fig4 a and 4b in fig4 a the utility box includes the vent exhaust fan 413 bypass branch line 411 with branch line isolation throttle valve 412 and the vent exhaust fan upstream isolation valve 414 in fig4 b the louvered utility box is in the same relative location but with the vent exhaust fan at a higher elevation no vent exhaust fan upstream isolation valve and the bypass branch line without a branch line isolation throttle valve any combination of the embodiments depicted in fig4 a and 4b may be employed depending on the intended approach to maintenance activities referring now to fig5 the flow path of the ventilation exhaust from the toilet rim as it enters through the vent exhaust orifices 511 travels through the ventilation exhaust annulus 504 out the rear vertical plane 516 of the toilet bowl as the annular exhaust vent line 515 to the low point drain line 507 through the upwardly sloped portion of the annular exhaust vent line to the enlarged connection 509 at the rear vertical plane 517 of the toilet and up through the parent exhaust line 508 vent exhaust fan upstream isolation valve 514 through the vent exhaust fan 513 and to the outside according to one embodiment of the present invention some ventilation flow also will exist through the bypass branch line 505 during vent exhaust.