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Discussion Starter #1
I've searched the forum but can't seem to find much on this topic. I have a 14 gallon tank that I will be mounting under the van. It will be used to collect grey water from sink and shower. The only fitting on the tank currently is a 3" waste hole where I plan to install a waste gate and a valve to allow me to dump when/where required.

I plan on adding an inlet on the top side of the tank to allow the grey water to enter the tank.

I would appreciate comments/answers to these questions:

1. What is the best way to add the inlet? I can reach inside the tank so I can add a threaded fitting, any ideas what I should use?

2. I assume I need to vent the tank. Can I just use a one way valve that allows air to escape, or do I have to create a vent stack? I hope it's not the latter as I'm not interested in running a vent to the roof of the van. Perhaps a cheater vent that I've seen used to vent kitchen sinks in islands?

Thanks
Shaun
 

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Shaun, I've been looking into the same thing. I did some googling and found several references that said the inlet does not need to be at the top of the tank (physics, water seeking a common level, etc). In fact, the inlet can share the existing outlet using a tee fitting. However, you still need a vent in the top of the tank. The vent doesn't have to be "stacked", but I don't think it should be one-way either. Air needs to flow in (drain) and out (fill). I plan on installing a single Hepvo valve between the tank and sink/shower junction, rather than a sanitary elbow. However, it should be above the tank-top level so as not to feel backflow before the tank is full. The Aussies are doing a lot of grey tank retrofitting now that their national parks have prohibited non-self-contained RVs (no grey water spills).
 

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Discussion Starter #3
Thanks Steve. I never thought of teeing off the drain to attach the inlet, that makes total sense and will eliminate another hole in the tank. I will just make sure the pipe coming into the tee is on the top side of the drain, and thereby higher than the top level of the tank. So are you saying the hepvo valve will serve as a vent? Won't that allow tank odours to vent into the shower (assuming no p-trap)?

Thanks
Shaun

Edit... or do you mean you will run a separate line with just the hepvo vent between the tank and the shower drain?
 

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2014, 138WB, High Roof, Gas, SW MT
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Hi Shaun,

I knew I would probably have to vent my grey water tank, but decided to try it without the vent. It does result in slow draining and a lot of gurgling, so I ended up adding a half inch vent at the top of the tank. The vent pipe only goes up a few inches and is just open at the top end. This has worked fine and I've not seen any sign of water coming out the vent. If I had to run the vent outlet higher, I'd probably just run it up into a fender well -- I don't think it needs to go to the roof as it does on a lot of RVs.

I would think about the low input to the tank. This will mean the inlet pipe will have water in it whenever the tank has a few inches of water in it. If things freeze up, the water in the tank input line will freeze. Granted the water in the tank will also freeze, but to me its a plus that with the high entry into the tank the inlet pipe will drain out (into the tank) and not be subject to freezing. We have had a couple times when the water in the GW tank froze for a while and then thawed with no problems -- not sure if this would be true for the inlet piping or not. You can add some RV anitfreeze to the GW tank to reduce the likelihood of freezing. So, I think either way can work, but something to think about.
I guess another issue with the low input pipe is whether it can be done without getting it so low it that it could be snagged on rough roads.

Gary
 

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So are you saying the hepvo valve will serve as a vent? Won't that allow tank odours to vent into the shower (assuming no p-trap)?... or do you mean you will run a separate line with just the hepvo vent between the tank and the shower drain?
A Hepvo valve looks/works just like those "cheater" vents you mentioned, except it's controlling water flow instead of air. It's made to serve the same function as a p-trap to keep sewer gas out of the RV. They just require less vertical space and they won't freeze. My plumber son says our (kitchen) sink and shower will be so close (back to back) they can share one p-trap (Hepvo).

I would think about the low input to the tank. This will mean the inlet pipe will have water in it whenever the tank has a few inches of water in it. If things freeze up, the water in the tank input line will freeze. Granted the water in the tank will also freeze, but to me its a plus that with the high entry into the tank the inlet pipe will drain out (into the tank) and not be subject to freezing. We have had a couple times when the water in the GW tank froze for a while and then thawed with no problems -- not sure if this would be true for the inlet piping or not. You can add some RV anitfreeze to the GW tank to reduce the likelihood of freezing. So, I think either way can work, but something to think about.
I guess another issue with the low input pipe is whether it can be done without getting it so low it that it could be snagged on rough roads.Gary
Good point about freezing. So Canada ain't Australia, eh? Bummer, now I have to find and maintain grade to the top of the tank instead. Or keep the tank empty if it might freeze. Might freeze = Canada.
 

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Most common way to ad ports to PE tanks is by spin welding. We vented our under vehicle grey tank underneath. Sink drain comes in the top and shower at the bottom due to routing convenience. Both flow well. We used the Hepvo traps near both sink and shower drains since the lines themselves can get cruddy and smell. Black tank vent goes up to the roof but its just a 3/4 " id hose terminating up to a cover-less hole at the top of the D-pillar. No smell ever. We do have a macerator toilet so that helps. One thing to consider is some tank rinsing sprayers. Tanks do tend to get gunked up over time.

Install notes and various photos in our build: https://sprinter-source.com/forum/showthread.php?t=27822&highlight=futon&page=52
Below. Our custom black and grey tanks (they are essentially mirrors of each other) that I designed, CNC'd and fabricated out of 6mm HDPE:



We used 1 1/2 " Valtera gate valves for both drains. Then added cam & groove fittings for attaching a hose. They are attached directly to the tanks so no drain plumbing to knock loose. (like I see on many commercial RVs)
 
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