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Old 01-14-2020, 01:19 PM   #1
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Grey Tank Confusion

Hey all, I'm having a hard time understanding the mechanics of getting the water from my showers and sinks to the grey tank, and I'm hoping someone can help clear up my confusion.

Basically what I can't wrap my head around is the order in which to do things.
My plan was to mount the grey tank without any holes and then cut a hole straight through subfloor and bus floor once I get to making the shower. However, with the grey tank mounted flush agains the ribs I'll basically have no way of cutting a hole and mounting a bulkhead to the tank except from above inside the bus. Is that possible? Are you supposed to cut your drain holes and mount bulkhead before mounting the tank? Is it better to just to mount the tank as the last thing after I've figured out exactly where my shower pan will go? I have a rough idea of a layout but there's no way I can preplan a shower in the middle of my bus down to the centimeter.

The only thing that worries me about doing the tank last is that I'll already have my subfloor down so I won't be able to bolt the tank through the floor.

My shower will basically be right on top of my grey tank.

Any help would be great thanks.

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Old 01-14-2020, 02:40 PM   #2
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Are you saying there is no space between the shower pan and the tank?

I’m not understanding what you mean by bulkhead.
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Old 01-14-2020, 03:06 PM   #3
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You can use flexible PVC and or hose if you're worried about placement. The key is that your grey tank that all your combined waste flows all the way to the tank. I'd be more worried about tank placement for weight distribution than for exact drainage location.
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Old 01-14-2020, 03:30 PM   #4
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You'll want to have a p-trap set up between your shower drain and your grey tank, like this: https://www.owasa.org/Data/Sites/1/m...am-9-11-14.jpg, which will require more than a 3" gap between the bottom of your shower stall and the top of your grey tank. Some people say a p-trap will dry out with infrequent use, which will allow tank vapors into your bus. YMMV.

Or if you can have some horizontal separation between your shower and your grey, you can use a hepvo valve like this: https://www.amazon.com/dp/B00NLMPLDU, which could probably fit with a 3" gap, but not with the grey tank directly underneath the shower drain.

I've been considering this trap for my own shower: https://www.amazon.com/dp/B00KEUQVGS

But basically, you don't really want to just run a pipe from your shower drain directly down into the grey tank.
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Old 01-14-2020, 03:37 PM   #5
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Originally Posted by Danjo View Post
Are you saying there is no space between the shower pan and the tank?

I’m not understanding what you mean by bulkhead.
I mean something like this https://www.rvpartscountry.com/Holdi...g-FPT-3in.html


There will be space between the shower pan and the tank because the tank will be flush against the ribs.

Picture my tank being flush with the driver's side battery box on the front, the inner frame and the outer skin on the sides, and the ribs on the top. Does that make more sense when I say I'll have no way to access and cut any necessary holes except from inside the bus?
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Old 01-14-2020, 03:50 PM   #6
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Here maybe these drawings will help visualize.

Click image for larger version

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Old 01-14-2020, 04:26 PM   #7
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Originally Posted by lebusmagique View Post
I mean something like this https://www.rvpartscountry.com/Holdi...g-FPT-3in.html


There will be space between the shower pan and the tank because the tank will be flush against the ribs.

Picture my tank being flush with the driver's side battery box on the front, the inner frame and the outer skin on the sides, and the ribs on the top. Does that make more sense when I say I'll have no way to access and cut any necessary holes except from inside the bus?
You can have a fairly sizable hole in the floor under the shower pan to make for access. Like 6x6 or so. If you know the size of the pan you need look online. You can find the exact dimensions you need to locate the drain center.

Get a P-trap that you will use. Get one with a Union. (Screw connection)

By measuring the p trap center to center you can tell where it will land.

From here you could try to locate the hole as a direct shot straight down, or you can offset the hole 8 inches or so. If you do the later, you can have a small lateral that you can later cut to length.
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Old 01-14-2020, 04:39 PM   #8
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I just saw the sink. Can you show orientation of the shower and sink with the grey tank under it and also draw the crossmembers (ribs) into it. This is important to determine the best way to do it
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Old 01-14-2020, 05:49 PM   #9
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you definitely want a P-trap.. a straight hole down will result in sewer odor.. grey water can definitely still put off some Stank...
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Old 01-14-2020, 06:44 PM   #10
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You will need an access hole large enough to put both hands into when the trap plugs up or you want to remove the tank for some reason.
Jack

Something like this:
.
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Old 01-14-2020, 06:54 PM   #11
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I just saw the sink. Can you show orientation of the shower and sink with the grey tank under it and also draw the crossmembers (ribs) into it. This is important to determine the best way to do it

Ok let's see if this drawing makes any sense. In my design the you walk in the bus and you're in the kitchen and if you look towards the back you see a wall with a long countertop going all the way to about 2.5 feet from the left side of the bus where there's a side aisle. Behind that wall is the bathroom. So, basically my idea was to have the bathroom sink drain pipe go through the back of the underside kitchen cabinets until it met with the kitchen sink, and then have both of those run into a t and then down into a single inlet on the grey tank.

The grey tank runs the left side of the bus between the axles, and the ribs are running perpendicular to it. I will definitely put some sort of trap under the shower.

I feel like my only option is to forget about mounting the grey tank all the way through the floor and just use a lot of self tapping screws into the ribs. this would allow me to run all my plumbing through the bottom of the bus, then raise the tank up, mark where I need inlets, then just pop them straight on to the drain pipes as I mount the tank.

Unfortunately there's just nowhere else for me to put the tank. It has to go here.
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Old 01-14-2020, 06:58 PM   #12
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You will need an access hole large enough to put both hands into when the trap plugs up or you want to remove the tank for some reason.
Jack

Something like this:
.
Didn't realize that was a thing you had to do either.

Hmmmmmmm. I don't really know what my solution is
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Old 01-14-2020, 07:26 PM   #13
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Didn't realize that was a thing you had to do either.

Hmmmmmmm. I don't really know what my solution is
Why does your grey tank need to be flush up against the bottom of the floor? I have the same problem as you only worse since the bottom of my shower will be six inches below the floor to begin with. My grey tank will be about 9" in height and suspended 11" below the bottom of the floor so it's flush with the bottom of the side skirt. You could basically gain as much of a gap as you need for a p-trap by lowering your grey tank.
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Old 01-14-2020, 07:51 PM   #14
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Think I just figured it out. I'll do a shower with a rear drain and use a smaller grey tank that leaves enough room on the skin side of the bus for me to work with pipes and such between the ribs.
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Old 01-14-2020, 07:53 PM   #15
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Originally Posted by musigenesis View Post
Why does your grey tank need to be flush up against the bottom of the floor? I have the same problem as you only worse since the bottom of my shower will be six inches below the floor to begin with. My grey tank will be about 9" in height and suspended 11" below the bottom of the floor so it's flush with the bottom of the side skirt. You could basically gain as much of a gap as you need for a p-trap by lowering your grey tank.
Even if I did that I would still have much of the same problem as the tank was planned to be placed such that it was flush on the front, back, and sides, making it all but impossible to do anything to the top once it's mounted.

Not sure why of all things this is what I'm struggling the most with wrapping my head around.
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Old 01-14-2020, 08:09 PM   #16
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Originally Posted by lebusmagique View Post
Ok let's see if this drawing makes any sense. In my design the you walk in the bus and you're in the kitchen and if you look towards the back you see a wall with a long countertop going all the way to about 2.5 feet from the left side of the bus where there's a side aisle. Behind that wall is the bathroom. So, basically my idea was to have the bathroom sink drain pipe go through the back of the underside kitchen cabinets until it met with the kitchen sink, and then have both of those run into a t and then down into a single inlet on the grey tank.

The grey tank runs the left side of the bus between the axles, and the ribs are running perpendicular to it. I will definitely put some sort of trap under the shower.

I feel like my only option is to forget about mounting the grey tank all the way through the floor and just use a lot of self tapping screws into the ribs. this would allow me to run all my plumbing through the bottom of the bus, then raise the tank up, mark where I need inlets, then just pop them straight on to the drain pipes as I mount the tank.

Unfortunately there's just nowhere else for me to put the tank. It has to go here.
That’s good to have those two drains tee together under the cabinet. Look at the “dual sink” drains commonly used for kitchen sinks. You might find those fittings helpful. .

I’m not understanding your terminology I’m afraid. Sorry! I think what you are calling a rib, I call a cross member. So were you thinking of getting the tank up inside the cross members so that it is in contact with the bottom side of the floor? I have done that for the black tank on my bus by taking out the battery compartment and pushing the tank through to the other side. But I have only done that because I am space constrained in a short bus. What bus do you have?

The cross members on my bus are 8” high, so there’s room to reach up in there provided there isn’t other bus stuff in the way. Take a look to see if you can get into the area from the side of where the tank will go.

How big will the tank be?

Have you considered the vent? You need to vent it. This is usually done by running a piece of 1 1/2” PVC or ABS up through a wall and through the roof. The pipe is capped with a vent cap that is glued and screwed to the roof. The vent doesn’t have to go directly into the tank it could be at the end of that waste arm for the sinks. It could be in the middle of that. It just needs to be a clear airway, free of p traps to the tank.
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Old 01-14-2020, 08:56 PM   #17
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That’s good to have those two drains tee together under the cabinet. Look at the “dual sink” drains commonly used for kitchen sinks. You might find those fittings helpful. .

I’m not understanding your terminology I’m afraid. Sorry! I think what you are calling a rib, I call a cross member. So were you thinking of getting the tank up inside the cross members so that it is in contact with the bottom side of the floor? I have done that for the black tank on my bus by taking out the battery compartment and pushing the tank through to the other side. But I have only done that because I am space constrained in a short bus. What bus do you have?

The cross members on my bus are 8” high, so there’s room to reach up in there provided there isn’t other bus stuff in the way. Take a look to see if you can get into the area from the side of where the tank will go.

How big will the tank be?

Have you considered the vent? You need to vent it. This is usually done by running a piece of 1 1/2” PVC or ABS up through a wall and through the roof. The pipe is capped with a vent cap that is glued and screwed to the roof. The vent doesn’t have to go directly into the tank it could be at the end of that waste arm for the sinks. It could be in the middle of that. It just needs to be a clear airway, free of p traps to the tank.

I think we're talking about the same things. By ribs I mean the hat channel running under the bus from side to side. Mine are only about 2.5" high.
I don't mean getting the tank flush against the floor, just flush against the channel/cross-member/rib. But it looks like I need to rethink that idea. I'm looking at a 50-60 gallon tank on my 24' FE bus.

Why does the vent have to go all the way to the roof? Can you have a 90 degree bend in the vent? Why can't the vent just stop underneath the bus?
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Old 01-14-2020, 09:11 PM   #18
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Watching more videos... Can you plumb into the side of a grey tank? I assumed you had to in through the top.
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Old 01-14-2020, 11:11 PM   #19
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I think we're talking about the same things. By ribs I mean the hat channel running under the bus from side to side. Mine are only about 2.5" high.
I don't mean getting the tank flush against the floor, just flush against the channel/cross-member/rib. But it looks like I need to rethink that idea. I'm looking at a 50-60 gallon tank on my 24' FE bus.

Why does the vent have to go all the way to the roof? Can you have a 90 degree bend in the vent? Why can't the vent just stop underneath the bus?
A 50 gallon tank weighs in excess of 400 pounds, so straps and self tapping screws won’t be enough support. You’ll find examples on the site of angle iron and all thread. Whatever you come up with should be substantial l.

The vent should go through the roof so there’s less chance of smelling it.
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Old 01-15-2020, 12:05 PM   #20
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Attachment 40773Don't know if this will help or not, but we didn't put a vent in the tank. We've got a 1 1/2" PVC drain pipe that dumps into the top of the tank and there's a 1/4" gap around the pipe. This works to vent the tank, and (surprisingly) there's no smell. The only time it's an issue is when it's full and we're moving, it splashes a bit out of the hole. I've put a towel around the pipe when we move and it solves the splashing problem.

This is all inside one of our luggage bins. The tank itself is strapped in with 2 ratchet straps that run the length of the tank and are supported by the lip of the tank. These straps go through the floor of the bus and under our bed. This was meant to be a temporary kinda "roof of concept" deal, but it's worked so well that I'm leaving the angle iron and allthread for a time when/if this fails.
House drain goes into the top of the tank at one end, and the tank drain is at the opposite end. It all looks and feels a little janky, but it's held up so well that I'm satisfied with its performance at the moment.
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