Toilet flusing problem. We have two baths back to back from each other as are the toilets. One flushes fine the other does not. But if we plunge it after we flush the handle it goes down fine. If we don't use the plunger the water ust swirls around. The on a rare occasion it will flush by itself but not as efficiently as the other toilet does. If there was blockage why would it flush at all even with a plumger or as I stated flush by itself on a are occasion. It makes no sense. Seems like if there was blockage it would not flush at all even with using the plunger. Could there be some kind of back pressure occurring or a vent pipe clogged.

That exactly what it sounds like to me. Either there is a clogged vent pipe, its not vented at the correct location or there's not a vent pipe at all.

It is vented through the roof. Looks like only one pipe for two toilets. Is that common. If the pipe was clogged up why would the other toilet flush OK?

It is vented through the roof. Looks like only one pipe for two toilets. Is that common. If the pipe was clogged up why would the other toilet flush OK?

It is common, however building codes are ever changing. It could be the position of the vent. It could be a clog in the vent or in the main line, even though it doesn't always make sense. How long has this been happening? Do you live in a single family home? If so, how old is your house?

House built in 1986. Been happening about 7-8 months now. How do you clean a vent pipe.

You can use a thin pipe snake (1/4" or thinner) or a garden hose works well at times. The snake needs to be able to make a 90' turn once it reaches the fitting. If it seems to be clear you can run a garden hose down it to flush anything that was in it. It shouldn't fill up, if it does, there's still a clog.

What's a pipe snake

It's a thin coiled wire made of spring steel with a small auger hook at one end. Its used to send down clogged drains to hook the blockage and pull it out or break it up. They cost $15-$20 and are available at most home improvement stores.