Several “S” trap drain configurations were observed during the course of inspection. In many locations, “S” traps are no longer accepted by the plumbing codes as these traps tend to easily siphon dry even when well-vented. It is recommended that further evaluation be obtained from a qualified plumbing contractor familiar with the local building codes. Repair or replacement should be conducted by a qualified plumbing contractor. The following link provides detailed information about proper drain configurations.
http://www.cdc.gov/nceh/publications/books/housing/cha09.htm
