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oups.com...
marson wrote:

you use a manometer (google "manometer plumbing inspection") a tube
connected to a manometer in inserted through the water in the trap of
the toilet. you blow on it to obtain a one inch difference in the
levels (i think, i'm not a plumber so someone might correct me), and it
should hold that difference. you need water in all your traps and your
vents must be blocked.

Thanks Marson, and Steve (below) for your help. A challenge for me is
that I don't have a manometer, and I really don't want to have to buy
one. The deal is, I (not the inspector) have to perform this test with
the inspector standing there watching me. I'm not sure I have a firm
grasp of enough of the details to do that.

A manometer is nothing more that a *U* shaped tube with liquid in the loop
and up the sides (any height should be OK). Why not get some clear tubing,
make a loop and put water in it. Fasten the loop to some plywood, make it a
foot or two long vertically. For the rest, one leg should be long enough to
insert into your toilet and the other leg whatever is needed for you to blow
into it without difficulty. Put some lined or marked paper behind the loop
and make some sort of scale so that you can measure the height difference
between the columns. Throw some food coloring in the water to make it easier
on the eyes. Of course, the height difference is a function of the liquid
that is used in the manometer. Many manometers use Mercury, because of it's
density, to keep the height difference to a manageable level. A column of
water 34 Ft. high is = to 14.7 psi. So, using water, a 1 in. height
difference is only 0.036 psi. (Another way to get the answer---Pressure=
height* fluid density).
Good luck
MLD