“Is it okay to keep our gray tank valves open all the time?”

We get asked that question plenty of times. In fact, it ranks right up there with “What tank additive should I use?” and “Why do I need your service? I already have a flush system in my gray tank.”

We’ve serviced hundreds — maybe even more than a thousand — RV holding tanks. And while no one should be leaving their black tank valves open for any reason, we’ve seen plenty of instances where gray tank valves are rarely shut.

What happens in these cases? Simple.

Think about that holding tank: A big, squarish, plastic box. The bottom of the tank slopes toward the front, where your RV’s sewer pipes collect waste to transport to your sewer hose and out into the RV park’s sewer system. That sewer pipe meets up to the holding tank at the front, or lowest part, of the tank. Waste exits via gravity (i.e. it goes downhill). However, waste also builds up along that low, front wall of the tank.

When your gray tank is full of water and waste, pulling or opening the gate valves releases the contents of the tank, effectively sweeping everything out (like suspended waste particles). When you keep the valve open, liquid slowly seeps out, leaving waste behind.

Is it a lot? No, probably not. But a few rice grains here, some soap scum there, add in coffee grounds, food scraps, and, over time, these start to combine into a sticky, rotting mess.

Leaving your gray tank valves open only invites problems later. A better solution is, just like with your black tank, to leave the gate valve closed, allow waste and water to collect until the tanks are full, then empty them periodically.