Odd Problem w/ Toto Drake - slower toilet needed?

Hi - first off, a big vote of thanks for Mr. Love's board; it's a tremendous resource. In large part because of the opinions here, my wife and I purchased a Toto Drake about a year and a half ago, and have liked pretty much everything about it.

BUT - there's a hitch. We live on the top floor of a 3-floor building with one condo per floor (the place was built around 1920 or so). Since the Drake was installed, our neighbors on the first floor have had a problem: whenever we flush our Drake, the water in their toilet surges and splashes around....very unpleasant if someone is sitting there.

We've asked several plumbers for their opinion, and everyone seems to agree that there's some sort of problem with the venting on the drain stack, but no one has offered a definite opnion on what would fix it. They all basically want to do exploratory surgery by busting open walls and looking to see what they can find. We've checked the vent pipe on our roof, and it looks fine, with no obstructions.

My guess is that the problem has to do with the rate at which the Drake sends its water down the drain - it takes just 3 seconds or so for all the water to go down; our old toilet (which was very scaled up from our hard water) took much longer, and there was never any problem. (Of course, that water flow is part of why the Drake is such a good product!).

We would like to solve the problem with a minimum of fuss and expense, so we're considering trying a different toilet - one that would take as long as possible to empty itself into the drain. I was at a friend's house recently and noticed that he had an older Eljer model that took about 12-13 seconds to empty; my guess is that something like this would solve the problem.

Anyone have any suggestions on a toilet that would take its time emptying and still be a good unit? Or, if anyone has any brilliant ideas for fixing our venting problem, that would be cool, too....I had figured a next step would be to take the Toto off its connection, and try experimenting by pouring 1.6 gallons of water down the drain at different speeds, and seeing whether slower rates made the problem go away.

Thanks in advance!

All new toilets use the 1.6-gallon flush by federal mandate. To do that, they all flush fairly fast. It is likely that that older Eljer uses more water than the new ones, so you could not buy or install one even if you could find an old one legally.

If I had to guess, and that's all it is, the building is wet vented, which is not up to current codes. This means that your drain line also is acting as the vent(s) for the floors beneath you. If this is true, then it could be some fairly extensive reconstruction to fix since new vent lines would need to be installed for each of the floors below up above your flood plane (typically 6" above the sink or 42" above the floor), or they could exit the roof on their own.

You could probably get the same result if you were to fill the tub, washing machine, etc., and then drain all of them at the same time.