I've been having some problems with my drains backing up. My bathtub fills up when my washer drains. My bathtub is slow to drain... sometimes not draining at all after the tub has been filled up. After reading many other peoples questions on this forum, I'm reading that the issue may be a blockage in the vent pipes. Is there a way to determine if it is from a blockage or whether the septic needs to be pumped?

If the tub fill when the washer drain the problem is downstream of both fixtures and needs rodding, not a vent pipe problem, that would be more for a slow drain. For now I am going to assume it is not the septic field, just for now. Do you have a clean out nearby or the washer or can you rod down through the washers drain pipe?

Im with Bob on this one. If it were a septic problem, all fixtures would cause a backup. Vent isn't the issue here. You need to auger the drain for the washer/tub. Any cleanouts available?