vacuum occuring?

I just installed to 2 new toto eco supreme toilets in the place of two older ones and they work great. water usage went down by about 700 gal/mo mostly due to no more multiple flushes.

however, when i flush one, the water level in the bowl in the other one goes down. there are no leaks anywhere, and verified the level going down by watching it as someone flushed the other toilet.

what do i need to do?

You must have a back to back installation.

The water will go from one side, over to the next, pushing air up into the other bowl, which causes the water to go higher in the bowl, and then when it drops, some goes over the dam.

Not much you can do unless you change the plumbing.

It does't hurt anything, but I've noticed it too.

back to back installation yes.

by the way, the toilets are the 1.28 eco supreme ADA height and length.

about the only annoying thing is going to someone else's house and forgetting they don't have a damper on the seat/lid, and BANG!!!!

NEVER have to flush more than once, and since i'm on a septic, we flush #1 after a few uses.

Thanks Terry.