Waste water tank capacity can vary from one RV model to the next. While both tanks are roughly the same size, the gray water tank will fill up much quicker than your black water tank (which rarely ever fills up). So keep an eye on your gray water tank level.
Keep in mind that your fresh water tank will probably be smaller than your waste water tanks. So even if you used all of your fresh water, you won't fill up either waste water tank.
How to know if your gray tank is too full?
If your gray water gauge reads "full", keep an eye on the shower drain. Your shower drain is usually the lowest drain in your RV. So if you see water spilling out into your shower, then your gray water tank is about to overflow. You should dump it as soon as possible or transfer some of it to your black waste water tank.
Equalizing your tanks
If your gray water tank level gets too high and you are not able to dump, one option is to transfer some of that gray water to your black tank. I don't recommend this as a general practice, but it can be done in a pinch to free up space in your gray water tank. There are two ways to do this.
- Attach a twist on bayonet valve (a.k.a. gate or knife valve) to the end of your sewer drain. With the valve in the closed position, open your gray tank valve and then the black tank valve. Your gray water will run into your black tank until the levels are equal (assuming the gray level is higher than the black). Your tanks will remain combined until you are able to dump.
- Buy a small portable pump and garden hose to pump gray water from your gray water tank to your toilet when your gray level gets too high. Be sure not to use that same hose for any other purpose.
- You could also drain some gray water into a bucket and pour it into your toilet. Be careful how much you release from the valve so you don't overflow your bucket. Open the grey valve then quickly close it and let the water in the hose pour into the bucket.
Valterra Twist On Waste Valve
Use this if you need to equalize your waste water tanks when your gray tank gets full. This twists on your existing sewer connection.