There is a toilet which doesn't flush solid waste fully. It just swirls in
the bowl without much going down the drain. (Thge same thing happens if
there is no solid waste in the bowl-the water swirls and while some goes
down the drain, the bowl doesn't empty as is normal). It worked better
before and is about 20 years old, though I can't find the date inside the
tank. The other drains in the bathroom and kitchen (which is nearby) are
ok. There is about a 5-7 foot run from the toilet drain to the septic
tank.

The small filler hole (I don't know what else to call it) that is at the
bottom of the bowl, right where the drain portion begins, appears to be
"salted up", that is it looks as if it is partially blocked, most likely
by growth of "salts" or other precipitation from the water/waste
combination. Is this the likely cause of poor flow?

I propose to test the main drain line by pulling the toilet, and pouring a
bucket of water down the drain. If this tests ok is it possible there is
something wrong with the vent stack (located in the wall immediately
behind the toilet) that is easily diagnosed? If the bucket of water test
fails I'll snake the drain.

My best guess is the "vent" in the toilet bowl. If this is the case, is
this easily cleaned out, or is getting a new toilet the best plan?

Thanks,

Charles