Modify gray tank to overflow into black tank. Has anyone ever done this?

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Mosagra

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For some reason I used to think that RVs were set up this way, if the gray tank fills up it would spill over into the black tank. It seems I am wrong.  Have been reading up on this, the gray water typically backs up into the shower and/or leaks and causes a mess.  Of course, the tank sensors are dodgy at best.

My tanks are:
Fresh water, 63 gallons
Gray tank, 60 gallons
Black tank, 55 gallons

It's pretty hard to fill up the black tank with the kind of trips we take, usually 4-5 days at music festivals where dumping tanks is pricey or impossible.  It's not hard to fill up the gray tank.  Would like to be able to pour 30 gallons or so into the fresh tank and not worry about dumping for a few days.

Has anybody ever tried it?






 
Easy to do. Just get one of these valves and put it on the end of your sewer pipe. Shut this valve,  then open the gray tank drain valve first then open the black water tank drain valve. The water from the gray tank will run over into the black tank until  it equalizes. This will get you a little bit of more time. Also, this valve will serve as a backup in case one of your drain valves are leaking buy a little.

http://www.rvplus.com/valterra-products-gate-valve-hub-spigot-t1001.html?gclid=CNvf9I_axcwCFcYfhgodGjAH3Q
 
Yes, I'm definitely going to try this secondary valve.  If nothing else it gives some protection from failure of the primary valves.

Thanks.  I found this video about the secondary valve, also.

http://www.gonewiththewynns.com/combine-rv-black-grey-tank
 
utahclaimjumper said:
Be careful about tying the two together,, I would not won't sewer gas coming thru the sink traps.>>>Dan
Click to expand...

How is it going to come through with water in the traps.
 
When you go up or down the mountains, the lower tank may run over.
 
Not an engineer but my gut feeling is this is a terrible idea. You only have 5 gallons extra between the two tanks. Not gonna gain much. Also the RV companys would utilize this idea if it had any merit at all. Their could be some obscure health codes which would prohibit these tanks being inner connected. Lastly if for some reason you over did it at your music festivals like getting stoned or intoxicated or trip out on LSD and forgot about the tank setup you would have nasty suprises in your shower pan which is the lowest drain opening in your rig. Just a thought.
 
It might be easier to divert one of the grey water sources to the black tank.
 
I might never need it, but I ordered one of the secondary valves. 
Really appreciate the tip on this, no modifications to rv needed.

http://www.rvplus.com/valterra-products-gate-valve-hub-spigot-t1001.html?gclid=CNvf9I_axcwCFcYfhgodGjAH3Q


IF I ever try it, will be sure to dump the tanks relatively soon once we start moving.

I haven't been intoxicated in about 35 years, but if I choose to do so will check the tanks first!  Maybe I'll put one of those reminder bands on the steering wheel.
 
Mosagra said:
I might never need it, but I ordered one of the secondary valves. 

http://www.rvplus.com/valterra-products-gate-valve-hub-spigot-t1001.html?gclid=CNvf9I_axcwCFcYfhgodGjAH3Q


IF I ever try it, will be sure to dump the tanks relatively soon. That is, once I come down off the drugs and the lsd.
Click to expand...

Just make sure you open the gray water tank drain valve first then the black water tank drain valve. Chances are all you'll have in the piping is gray water.  Then shut both valves until you're ready to dump.
 
I installed the third "master" valve on our current motorhome as well as the previous one. I've found it works quite well for using a nearly full grey tank to give the black tank a rinse after dumping. With the master valve open, I dump the black tank normally, leaving the valve open. Next I close the master valve and open the grey valve, allowing the usually soapy water to equalize into the black tank. Once that happens, I close the grey valve and open the master to drain the black tank again, followed by opening the grey valve again to rinse the waste hose. All valves get closed when done of course.

I haven't used the master valve to equalize the two tanks to extend the capacity yet, but I wouldn't hesitate to do so if the need arose. Residential plumbing and septic systems have worked just fine for a lot of years with just a single tank and common vent. Many RV's in fact do have a single vent that serves both tanks, and some high end RV's only have a single large waste tank, as do most large tour buses used by celebrities, etc.
 
Thanks for this tip as well.  I certainly can't think of any downside to owning this $28 device.
 
Howdy Rene, Dutch, Mosagra,

Rene T said:
Easy to do. Just get one of these valves and put it on the end of your sewer pipe. (...)
Click to expand...

NY_Dutch said:
I installed the third "master" valve on our current motorhome as well as the previous one. (...)
Click to expand...

Thanks everyone (including the OP for having asked it), this seems to be a great idea as it serves three very useful purposes (equalize volume between the two tanks, work as a backup in case one of the other valves are leaking, and for flushing the black tank).

This may be a stupid question, and if so I apologize in advance, but how is one supposed to install that on the sewer pipe? Permanently, using pipe glue or something similar? And how is the sewer hose supposed to be attached to it, as I see no "clawed thread" no anything?

Thanks in advance,
--
  Vall.
 
One side of the valve has the same makeup as your sewer hose so you just lock it on your pipe and the other side has the makeup to accept your hose.
 
Hi Rene,

Rene T said:
One side of the valve has the same makeup as your sewer hose so you just lock it on your pipe and the other side has the makeup to accept your hose.
Click to expand...

Thanks! This solves it... I only asked because it can't be seen in the photo.

Cheers,
--
  Vall.
 
The link Rene posted is for a permanent connection.

This is the twist on one you would need.

http://www.amazon.com/Valterra-T58-Twist-On-Waste-Valve/dp/B000BGHYJS

Or if you want to buy from rvplus:

http://www.rvplus.com/valterra-twist-on-waste-valve-t58.html
 
Rene T said:
One side of the valve has the same makeup as your sewer hose so you just lock it on your pipe and the other side has the makeup to accept your hose.
Click to expand...

Just to be sure I'm not confused, this is the valve you are describing,correct?

http://www.rvplus.com/valterra-products-gate-valve-hub-spigot-t1001.html?gclid=CNvf9I_axcwCFcYfhgodGjAH3Q

After thinking about this for a day or so, I think I like the idea and am going to try it.
 
The valve in that link is a permanent mount valve for the 1.5" gray tank.

You need this one:

http://www.rvplus.com/valterra-twist-on-waste-valve-t58.html
 
Abendage linked to the correct twist-on valve. Since mine is a semi-permanent installation, I locked the twist-on in place with a short self-tapping screw behind one of the "dogs". My setup also has a 45 deg. clear twist-on elbow, also locked in place with a screw, attached to the valve to bring the hose connection outside of the waste bin. A safety cap goes on the outside connection point while underway as required by law.
 
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