Question

crown - vented traps
are recommended on the upper floors of houses
are used on double trap situations
are not permitted in most areas
are always more than two pipe diameters from the trap
are used on drum traps
question 24
a trap primer
is used on every trap
requires an air gap
prevents traps from freezing
uses mineral oil
prevents traps from siphoning

Explanation:

Crown - vented traps are typically used in double - trap situations to ensure proper venting and prevent siphoning. A trap primer is used to prevent traps from siphoning by maintaining the water seal in the trap.

Answer:

For the first question: are used on double trap situations
For the second question: prevents traps from siphoning