I have not seen this in over 40 years. Brand new toilet.(we tried 3)As soon as you tighten it down it will not flush. If you loosen the bolts abd allow a little air to get past the gasket and the flange it will flush as per normal. Tighten the bolts---no flush. Already snaked the drain and checked with camera --no problem. Old toilet worked for 15 years--retiled floor and walls, nothing will flush.

Looking for possible answeer anyone!

Maybe the old original one did have a leak that allowed air to suck in but not leak water? And you have a blocked or restricted vent?

Tell me how it won't flush. Water goes into the bowl raises to the top and swirls around before slowly draining away? Backs up and runs over? Will take down liquids but not solids? More details please. Tom

Tell us why you replaced the original toilet too please.