I am remodeling a bath and need help with a possible venting issue. Over the past several years the shower drain gurgles when the toilet is flushed. The house was built in 1968. The bath has been gutted so I thought now is the time to investigate the problem. It is an upstairs bath that was all original. Is the vent clogged? Should I have it snaked through the toilet and shower drain? I never had a problem with the toilet being clogged in use. Please help.