You have settled into a full-hookup campsite, hooked up the water, plugged in the power and connected the sewer hose between the RV and the campsite sewer inlet. Seasoned RVers know you always leave the black dump valve closed* until you are ready to dump the black tank, but what about the gray valve?
Many RVers like to leave the gray valve open so they can liberally use the shower and run sink water without having to worry about filling up the gray tank. However, doing so can allow sewer gases to travel from the sewer system up your sewer hose
and out the gray tank plumbing vent located on the roof of your RV. While it is unlikely you will smell the offending gases from inside your RV, it is very likely anyone in the vicinity of your RV will. Not the best first impression to make with your fellow campers!
One solution is to leave the gray valve closed until you need to dump the gray tank and then close it again. This can become tiresome if you are camped in the same location for weeks or months on end. The best solution is to arrange your sewer hose so it forms a P-trap. The standing water in the trap will prevent sewer gases from traveling up your sewer hose into your gray tank, but still allow gray water to freely pass down the sewer inlet. This allows you to keep your gray valve open without being an odiferous offender to your neighbors. Many times the campground sewer hookup is elevated off the ground, providing an automatic trap for those that leave their sewer hose on the ground. If not, running your hose up and over a couple of blocks, higher that the diameter of your sewer hose, is sufficient.
Final note: A day or two before you leave camp, close the gray valve and straighten your sewer hose to remove the trap or place your Slunky sewer hose support under the hose. When you are ready to break camp, dump your black tank and then flush your sewer hose by releasing the captured gray water. This rush of gray water will easily flush out any solids that may have collected in the low spots while the trap was in place.
*Unlike your home toilet that uses a large amount of water with each flush to carry waste down the pipes into the sewer, a RV/Marine toilet uses just enough water to rinse the bowl and allow the waste to drop, via gravity, into the black tank below. Leaving your black tank valve open allows the liquids to drain out of the tank, typically leaving the solid waste behind to accumulate on the bottom of the relatively flat holding tank. Soon you will have the dreaded “pile of doom” solidifying on the bottom of your black holding tank. If left to dry and harden, you may find yourself taking your rig to a RV dealer to have it professionally removed. Always leave the black tank dump valve closed until you are ready to dump. When dumping, the rush of accumulated water exiting the tank will carry the solids out at the same time.