Went to lake house and discovered that the toilet doesn't flush good. Sometimes it requires plunging. We have a big flush volume type toilet. Sinks seem to drain properly. Toilet was installed last year with a new shower. All was working well last year. We haven't used the toilet in a couple of months.

We are on a septic tank.

The sinks seem to drain well. I fill the sinks up and they drain as usual, not slow, not fast.

The house has no sewage flush plug. Built in 1970.

Any ideas before I call Roto Rooter?