By Doug Swarts
In the last issue of RV Travel we commented on three sewer hookups at RV parks. No one took issue with photo #1 or photo #3. But photo #2 started a conversation regarding using the sewer hose at the sewer inlet end as a p-trap.
IF you feel adding a water trap in your hose will prevent sewer gases from entering your RV you must be leaving your gray tank or tanks open for it to have any potential effect.
IF you keep your gray tank closed, as most RV waste management experts recommend, and only open when using the clothes washer or dumping tanks, you have NO need for a water trap. Notice I say water trap, NOT p-trap. That’s because most p-traps are designed to equalize water in the pipe so NO air can get through unless the returning air is more than 3 to 4 psi, at which time the gases begin to filter through the water and back up the pipe into the sink.
Without actually measuring the trap in photo #2 it is difficult to say whether the hose in the droop is actually full with no air space at the top of the hose.
Does having a water trap in your hose cause any negative effects on the dumping process? Probably not, other than potential wear on the bottom of the hose and the need to “milk” the hose before storing it.
Standing water in the hose, however, will permeate it with odors that cannot be flushed away and decreasing the life expectancy of the hose. The water trap does little to prevent sewer “critters” from entering your gray tank, which is reason enough to keep the gray valve closed!
For the reasons stated above, I would not add a water trap in my hose, but then again I do not leave my gray tank open unless the washer is in use or I am dumping my tanks. I also feel that the less time water is in the hose the longer it will last and the cleaner it will stay.