Interesting.....

I believe double trapping has the potential to cause future problems. In which case, I would highlight it to my customer.

When two traps are hooked up in series the potential issue is not siphoning but that the traps will tends to clog up more frequently.

When traps are in parallel you could have the potential for a venturi effect and water could be siphoned out of one of the traps under certain conditions. I would think that under most conditions that this is an unlikely scenario. However, with today's deeper sinks and two sinks draining at the same time, we could see a problem occur.

Jeff Euriech
Peoria Arizona