Low-flush toilets are generally classified into two categories. Gravity-flush toilets are like standard toilets but are designed to use less water for flushing. The smaller amount is compensated by siphon jets and the flush valve using more force to push the waste into the drainpipe.
The second class of low-flush toilets, the pressure-assist model, works on drainpipes that are not properly sloped; your Edmonton plumbing expert may recommend such an installation if the evaluation of the drains reached the same conclusion. Standard drain slopes are set at 1/4th of an inch per square foot for three- or four-inch drainpipes. Pressure-assist toilets work by using compressed air to push the waste down the bowl and through the drainpipe, thus eliminating the danger of water backup.