Question

all of the following may cause traps to lose their seal except
dumping mineral oil down a drain
indirect siphonage
backpressure
evaporation
capillary action
question 38
leaks in drain pipes are commonly caused by all of the following except
poor joint connections
damaged piping or traps
missing air gaps
freezing
clogging

Explanation:

1. For the first question about traps losing their seal: Dumping mineral oil down a drain can break down seal - related substances, indirect siphonage can remove water in the trap (breaking the seal), back - pressure can force substances through the trap and disrupt the seal, evaporation can dry out the water in the trap (breaking the seal). Capillary action has little to do with a trap losing its seal.
2. For the second question about drain pipe leaks: Poor joint connections, damaged piping or traps, freezing (which can expand and crack pipes), and clogging (which can cause pressure build - up and leaks) are common causes. Missing air gaps are related to preventing back - siphonage and cross - contamination rather than directly causing leaks in drain pipes.

Answer:

1. Capillary action
2. Missing air gaps