sharing gray tanks

You didn't mention which tank fills first. My grey bath water fills quickly, so I set up a grey water toliet flush system. I add my black water chemicals to the grey tank before use. Works very well, no additional smells and chemicals are constantly "metered" into the black tank. I also use less fresh water and extend my stay by two days.

F14man wrote:
Seems like we fill one tank before the other is 1/3 full. Anyway to share the tow as one tank?

As the previous posters have written, sharing the two grey tanks is easy with a shut off valve on the outlet. This is great when boondocking.

But you didn't tell us what rig you have. Newer RVs have "dropped" frames. The manufacturers may put the two grey tanks on different levels. If you try to "share" these tanks, the lower one will fill first and be subject to excess pressure as the upper tanks fills. I wouldn't stress one these cheap tanks that much.

Itching2go wrote:

bpounds wrote:
Yes. Maybe. If you have one single dump outlet, you can add a blade valve right at the outlet. Then leave your two tank valves open, and the level will equalize between the two. If you have two separate dump outlets, there won't be a clean and easy way to plumb them together outside the coach.

Many of us have added that blade valve at the dump connector. I use it to back wash my black tank using gray water at the dump station. It is the same concept, which is to let the tank levels equalize.

This is the only method that I'm aware of, but you do need to have a single dump connection equipped with a blade valve there for this to work. We needed to use this method a couple of times with our previous rig. Our current rig doesn't have a blade valve at the outlet (yet). Something I plan to fix. ;)

Sounds like the way to go. Thanks.

F14man wrote:
Seems like we fill one tank before the other is 1/3 full. Anyway to share the tow as one tank?

Depends on how much effort you are willing to make. Drop the underbelly fabric and add a 3/4" or 1" line between the two gray tanks. Could be rigid or flexible line and the high point of the line will determine at what level sharing is initiated between the two tanks. Also a level trailer will also be critical. Of course you will have to add fittings either to the tanks or the existing drain lines prior to the blade valves.

Another possible option is to use drain caps that have built-in 3/4 " hose fittings and just use a garden hose between them. Both gray valves must be open and the black valve closed. And if either of the valves is a long distance from the outlet, there will be a significant amount of gray water to deal with when disconnecting everything.

All three of my waste tanks dump via one common drain line.
I installed another drain valve on horizontal run just before elbow where line turns outward.

With it closed I can equalize both grey tanks (galley would always fill faster than grey) giving me 78 gallons of grey tank capacity.
After dumping black tank I can close added valve then open grey valves and flush grey water into black tank for a flush.
With added valve closed I can equalize ALL three tanks and have 128 gallons of waste tank capacity. (Wasn't that long ago RVs only had 1 tank)

A 'twist on' valve is available but it would stick out too far on my 5vr and would need to be taken off/stored for travel.........permanent install was cheap and easy.

The 'twist on' style could be used with rigs that have 2 dump lines and a 'Y' connection.

bpounds wrote:
Yes. Maybe. If you have one single dump outlet, you can add a blade valve right at the outlet. Then leave your two tank valves open, and the level will equalize between the two. If you have two separate dump outlets, there won't be a clean and easy way to plumb them together outside the coach.

Many of us have added that blade valve at the dump connector. I use it to back wash my black tank using gray water at the dump station. It is the same concept, which is to let the tank levels equalize.

This is the only method that I'm aware of, but you do need to have a single dump connection equipped with a blade valve there for this to work. We needed to use this method a couple of times with our previous rig. Our current rig doesn't have a blade valve at the outlet (yet). Something I plan to fix. ;)

We use a plastic dishpan and catch the water from the galley and pour it down which ever tank has the most room, black or gray when we are boondocking, use it for flushing also.

F14man wrote:
Seems like we fill one tank before the other is 1/3 full. Anyway to share the tow as one tank?

Take more showers!!!:B

I am careful with the galley tank, conserving water for rinsing, and take lots of showers.
this way the tanks seem to fill at about the same rate. I then use the tanks to flush out the stinky slinky.

Dump black first.
Then Galley, water can be a little greasy.
Then the clean soapy water of the Grey tank, just Shower and bathroom vanity.
When all dumped the slinky is clean!

Yes. Maybe. If you have one single dump outlet, you can add a blade valve right at the outlet. Then leave your two tank valves open, and the level will equalize between the two. If you have two separate dump outlets, there won't be a clean and easy way to plumb them together outside the coach.

Many of us have added that blade valve at the dump connector. I use it to back wash my black tank using gray water at the dump station. It is the same concept, which is to let the tank levels equalize.

Depending on rig brand. Not on my Montana.