Grey (gray) tank leak

[Roly]

Additional thought: Fabricating a unique piping solution via 3D printing with ABS filament could be more feasible than fiberglass layup.

Roly

[Blue~Go]

Roly,

Thanks for the kind words. It's great to see some familiar names still here (plus some new ones!).

Good point on the 3D printing. So many cool/custom things you can make that way. For me, fiberglass is something I've done a fair bit of and I have the materials on hand; whereas 3D printing is mysterious and I don't have any supplies. Wish I did though! Maybe in future.

For this situation I think what would be perfect is a 90º elbow just like what was there originally, only with a hub (female) only on one side --- the side that connects to the incoming plumbing. Then on the side that goes into the tank, it could be like a street elbow (no hub, just pipe diameter) only it should be longer than normal. Long enough to go in through the grommet and then clear the inside of the grommet by maybe an inch or so [Edited to say: Or maybe only 1/2-3/4" -- I forgot this is also the vent, so any amount it sticks down into the tank is essentially lost capacity].

Then one could use a hub/hub Fernco on the crack-prone joint (which might actually be preferable to the original ABS/glue/ABS) and the other end could just cruise in through the grommet.

The "problem" with fiberglassing (and why I'm considering the short "vent" elbow instead) is that with fiberglassing it's easy to make one side smooth, but then you'd typically have more material on the second side. It has to be somewhere! But with this you don't really want extra material on the inside (water flow) or on the outside (grommet fitment). 3D printing would solve that - cool idea.

Here are the dimensions of the three common hub/hub ABS elbows. IIRC, Chinook used a normal sanitary ell there (so not a long sweep, and not a short turn either, but the middle bear). If I'm figuring it right, that means the short ell would gain about 3/4" in "height" for there to be pipe between the downturned hub and the grommet. So not the ideal gain, but better than nothing. Probably wouldn't be advisable if one is the type to fill both sink bowls to the brim and then pull the plugs simultaneously; but I think for most typical Chinook use it would be okay. This does carry the shower drain water too. However TP and other larger stuff of course doesn't take this route since it's going into the black tank. Wish it was more gain though. If Chinook had used a long sweep elbow (which should technically be used), then we could have gained more by switching to the short ell.

Maybe I'll re-visit my fiberglassing idea, with the idea of putting the extra material on the outside (where it would mash into the hub), but keeping it relatively thin and streamlined. Certainly would be an improvement over having a full sized hub crusing its way in there. Tho nothing changes the fact that there is very little vertical room to work with.

My other thought involved a Hepvo trap for the shower. I could see three advantages:

1) No water in there to freeze (because imagine the horrible project it would be if that shower trap froze).
2) I have had the shower trap siphon empty while driving, which allows grey tank odor into the rig -- doesn't happen with a Hepvo trap
3) That whole run could be basically tight to the floor (as it is right at the break/strap point). I guess that wouldn't totally change the problem of the elbow and the grommet clearance though.....

As a reminder, here is what we are working with. I note that the drain piping is also acting as the tank vent (but not via the proposed Hepvo leg, which is pure drainage).

First drawing is 1998 manual. Less cluttered as they don't show all the details of the pipe sizes. Blue area is the "mess" of pipes leading up to the crack-prone spot. Red arrow shows the exact crack spot.

Second drawing is the same area from the 2000 manual. A bit more cluttered but they show the pipe sizes and fitting types.

Lastly, a very clumsy drawing showing the concept of using a Hepvo trap on the shower. Not sure this really solves the "last drain elbow to hub" height problem though. So point #3 is less impactful. But might be something to consider if dropping the grey tank anyway. I haven't fully worked this out in my mind though, so it's just musing at this point.

BTW, if anyone is going to make an access hole for this project, I can give some measurements. I already made the four corner holes and cut through the first layer of flooring (which, I then found out, that the floor there - at least in a 1999 - from the top down is 1/2" plywood, 1/2" white bead type foamboard, (then I think I will find) 1/2" plywood, and a layer of fiberglass cloth/resin, tho I have not cut out the bottom plywood layer yet. I have cut the intial square out of the top layer, which I may or may not expand.

What I'm thinking is to make the top cut a little larger than the bottom one. Then epoxy cleats into the sides (between the two layers where the foam was), and then make up a "plug" that will be larger on the top than the bottom so it can't fall through. Then screw that down. Maybe there will be a next time and maybe there won't, but the plug shouldn't hurt anything if there isn't --- and if there is it will be there.

I've been thinking that first I will try to make the repair from the top (access hole). If it's too difficult (a little bit of it would still be under the shower so not 100% clear access), and the tank still needs to be dropped; then I think it would still be useful on the re-install to be able to have one person inside the rig pushing down on/steadying that elbow while the second person pushes the tank up from below. From the access hole one could also possibly guide the tank a bit so the elbow and the grommet line up, which the person wrestling with the tank would not be able to see at all.

BTW, how I figured out where to put the access hole was by a lot of measuring, then some really positive thoughts, then drilling an initial (forward/passenger side) hole all the way through and pushing a zip tie down into it, then going below and seeing where the zip tie came out (not in the elbow was the goal, success, whew). Then repeat for another zip tie for the second (aft/passenger side) point. The driver's side was then the same fore-and-aft and limited by the shower wall on the driver's side.

[Blue~Go]

I had a thought this morning: I remember a fellow boater making "custom" hard elbows for his sanitation plumbing by using some (happened to be clear) rigid 1-1/2" tubing from McMaster-Carr and custom bending it by heating it up. Hmmm. There's no particular reason the end that joins to the rest of the incoming piping has to be a hub. There are Hub-to-spigot Fernco's just like the Hub-to-Hub (I purchased one of each, since I wasn't sure what would work out best).

If that tubing would work, then I could just bend an elbow with "tails" as long as needed. And no hub to mash the grommet. I'll have to see if the OD is close to the same as ABS since it needs to friction fit with the grommet. If I can find the part number, perhaps I'll order a length and check it out. Already have two grommets on hand.

Edited to add: The OD of 1-1/2" ABS DWV pipe is 1.9" (aka 1-29/32") -- so that's what the tank entry grommet will be expecting.

[Roly]

I see some fat radiator hose with a 90 degree bend available in the world wide web, maybe a cobble up of that and exhaust hose and obscure hardware could do it.

Roly

[Blue~Go]

I see some fat radiator hose with a 90 degree bend available in the world wide web, maybe a cobble up of that and exhaust hose and obscure hardware could do it.

I don't think that would end up working (though I like your thinking outside the box). Here's why:

The grey tank doesn't have a "neck" that sticks out, like say you would see on a plastic fuel or water tank (or a radiator). Instead it simply has a circular hole cut in the top. Into that hole goes a large grommet. Into the grommet goes a rigid pipe of 1.9" OD. I don't think a "soft" pipe would interact properly with the grommet, which is meant to sort of stretch/lock around something hard. This is a typical waste tank entrance.

The real issue is that there is just not enough clearance between the top of the grey tank and the floor of the Chinook to do anything really easy/proper/off-the-shelf. Now, the originals seem to last 20+ years, so that's something. But, it was a slightly compromised installation. Perhaps it would have been better to have a recessed notch in the tank (as there was in the original fresh water tank where the fill entered) to accomodate the fittings. OTOH, that would put the grommet under more pressure (to leak), so perhaps that's why not on a waste tank.

I'm now thinking that bending up a section of 1.9" OD tubing would be the way to go. Nice gradual bend, nothing wider (like the hub of the ABS elbow) to try to mash into the grommet. Then use a Hub-to-spigot Fernco at the crack-prone joint, so the tiniest wiggle won't try to crack it again. Or, same concept but with an off-the-shelf short elbow and X" of pipe glued into it on the tank side (would hold hub 3/4" further above grommet top). Same Fernco joint except with a hub-to-hub Fernco.

Here is what the grommet looks like. The tank just has a hole drilled through the middle of the flat top surface

[mendodave]

That is the grommet I used. It has a stop on the interior at 1-3/4s down. The pipe is 3-1/2" long. Your tank got bopped up, all right!
my block at the elbow is only 1/2", I need to make it thicker. The next block upstream is 3-1/4" thick. It must be thicker than that to flow properly, unless I am looking at it upside down and backwards!

you can see the friction wear on the downpipe.

I am not quite sure how a hatch will work with all the attached plumbing under there...

David

[caconcourse]

Roly,


For this situation I think what would be perfect is a 90º elbow just like what was there originally, only with a hub (female) only on one side --- the side that connects to the incoming plumbing. Then on the side that goes into the tank, it could be like a street elbow (no hub, just pipe diameter) only it should be longer than normal.

Hi Blue,

It turns out they actually make ABS "street elbows", like this one: https://www.etrailer.com/RV-Sewer-Hose- ... gKFWfD_BwE

[mendodave]

Tank is installed...
two or three people would have been better, one person....not so much
I took off that hanger strap, and no block, so there was less pressure on it, it seemed better to leave unstressed.
That entire downpipe at the end is inside the tank, the elbow butts up against the grommet, as in blu-go's post

Bill's instructions for his grommet said to use butyl caulk around grommet and tank, I did not have any, but I did have RV butyl tape, so I used that.

seems very snug, and NO LEAKS!
the new ValTerra valves are worth it, I think $50 or less for both.

now, the entry door....

David

[Blue~Go]

Hi Blue,

It turns out they actually make ABS "street elbows", like this one:

Hi Clay,

I left on a trip just after my last post, so never saw this. Yes, this is what I was saying would be great, BUT if the "street" side of the elbow was quite a bit longer (and then we could cut it to the perfect length, but that would be longer than the typical street elbow you linked to).

Otherwise, short of anything custom, one needs to use a normal elbow (hub x hub) and then glue a length of pipe into it, like Mendodave shows above (as Chinook did). A short hub x hub would buy a tiny bit more height, but nothing major.

Mendodave: Yay, great to hear your repair worked well.

BTW, my tank didn't really get pushed upward (it's still tight to the metal brackets just like it always was). I mean, yes it was momentarily "bopped" as it touched the grass hump, but I believe that only cracked the pipe because it's ancient ABS in a stressed position, and kind of a built in stress riser -- because there is like 1/16" inch of pipe between two glued hubs. I have some photos of the plumbing from many years ago, and that elbow/hub was already sinking into the tank grommet (just due to lack of space in the design, I think). Maybe that's what you meant though.

Anyway, it's not the greatest setup by design, but then no-one wants the floor of the rig any higher or the ground clearance to be any less. Too bad there were not Hepvos in use back then for them to have used - would have helped some.

I still have on my list to see if I can do a similar repair through my "trap door," but nothing to report yet.