I hope someone can tell me what else to try. I am redoing a bathroom in a 50 year cabin. The old toilet flushed strong, but there was a "gurgling" in the other drains. When I removed the old toilet I replaced the flange. The old flange had 3" pvc inserted into the 4" cast drain with some plumbers putty sort of filling the gap.

I installed a new flange with a "two finger" gasket into the 4" and it is sealed tight. I installed the new toilet and when I flushed, the bowl would quickly fill with water and then slowly drain down to the proper level (in a minute or so). I pulled the toilet and set it up on some 2x4s in the back yard, filled the tank with a hose and flushed it several times. Not the problem, flushes great. I then dumped 3 or 4 gallons of water directly down the waste openning and the water all went down quickly. No clog there. I reinstalled the toilet and the same "slow" flush is still there.

I assumed I had a vent problem so I dragged a hose up to the vent exhaust on the roof and ran water into the vent for 5 minutes (3" vent pipe, 15' long). I assumed it would fill up if there was a clog in the vent would it overflow on the roof but the water drained down the pipe fine. I even snaked the hose down the vent for its entire length and the water ran through fine. But I still have the "slow" flush.

I should add that if I fill the kitchen sink and drain it, the water in the toilet bowl goes "lap, lap, lap...".

I'm still thinking this is a vent problem but at this point I don't know how to proceed.

Any ideas on what to do next?

Thanks in advance,
David in Missouri