I bought this house, the ground-level toilet would not flush. Sometimes a burp of air would come up, then the water would swirl around and not go anywhere. Sometimes just the swirling without the burp. We snaked up from the basement as far as possible. We snaked down the toilet. We checked the vent by snaking down from the roof. Pouring a bucket of water into the bowl resulted in a complete flush. I was told it is probably that the toilet has build-up from years of use. I bought a new toilet. It is acting the same way. A big burp of air comes out from the bottom of the bowl, and the water swirls around and around. This is the "optum vormax" American Standard toilet. It doesn't always burp the air, but it always swirls around like it will never go anywhere. If you hold the handle down, you can get all the water to eventually go down, but there is no power behind the flush at all. Any ideas how to fix this problem? I would appreciate your help. Thanks.

IT sounds like the toilet was installed over a "P" trap, but that would mean that the original installer did not know what he was doing.

Or that there's a belly in the piping downstream of the toilet, before its vent.

It would have to be a BIG one.

There is no p-trap or other impediment in the exit route. There is a shower p-trap about 12 inches downstream from the toilet (on the way to the septic tank). The vent is between the two.