. . . No, not to pour down the toilet but to pour down the drain of one of the sinks that connect to the same pipe that goes out through the basement wall.
The sinks seem to drain OK, but the toilet typically takes two flushes to clear semi-solid waste and makes "glug glug" noises that the other toilets (connected to a different pipe) do not make.
I have used a snake on the toilet, but there is no sign of anything being dislodged.
MB