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Old 12-20-2013, 02:40 PM   #1
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Inca Plastics Did Great

I'm rebuilding the drain plumbing in my 66 Trade Wind. I need two new tanks, black and gray. Inca has a catalog of scores of tanks they supply to RV manufacturers. I reviewed the catalog and found tank H57 that fit my frame bay under the bath. It is narrow at only 19" wide by 54 long. I ordered two of these 25 gallon tanks.

Inca was very helpful on the phone. They also provided rubber grommet seals and the toilet mounting flange and seal. The tanks were delivered a week later.

They fit up well and will work well for my Trade Wind project.

Good job Inca Plastics. I was pleased with their product and service. They may be able to help you with your project.

David
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Old 12-31-2013, 06:46 PM   #2
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Picture of the Tanks

Here is a photo of the tanks as delivered by Inca. I like the mounting ledges. I can set the tanks on angle irons and secure them to the frame rails.

I will be using the Inca rubber grommet inlet seals. This is what they provide to other RV makers. This allows more flexibility in drain pipe location.

I worked in a roto molding shop for 4 years. We used rubber grommets in customer's fuel tanks. They seal up great.

David
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Old 12-31-2013, 08:58 PM   #3
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The black tank is on the right, correct? If so, then you don't want the outlet of the tank reduced to 1-1/2" - you want to keep it a full 3" to the dump valve and sewer hose connection. The gray tank typically has the 1-1/2" outlet.

Other than that, the tanks do look nice.

Chris
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Old 01-01-2014, 05:50 AM   #4
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Hi Minno,

The black tank is on the left. It will have the full 3" diameter dump port. INCA installed the 3 to 1 1/2 diameter reducer in the gray tank for me. They said 1 1/2 drain plumbing is normal practice for gray water. My 86 trailer is all 3" on the discharge sides of the tank. I'll use a 1 1/2 and 3" sanitary Y to join the discharge ports together and then connect to the "slinky" to the sewer connection. I will use Valtera valves as I prefer their seal design, pipe connection flexibility and parts availability.

The gray tank will have two vent lines: one for the kitchen sink drain pipe about 7 feet upstream from the tank inlet on the street side, and one for the shower pan about 3 feet upstream from the tank on the curb side. There is no direct vent line on the top of the gray tank.

Do you think the gray water tank will drain normally through a 1 1/2 pipe with the vents located upstream in the pipes? I can easily change the gray water holding tank to 3" discharge now. It would be a bunch harder after it is built up.

I can hear some significant gurgling when I drain the gray tank on my 86. The vents are located on the curb side and on top of each tank. The discharge port is on the street side as normal.

David
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Old 01-01-2014, 12:31 PM   #5
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Hi David,

I thought the black tank was on the right since it has the toilet flange sitting on top of it.

Yes, the gray tank will drain fine though a 1 1/2" drain pipe. Sounds like the tank vents are also drain lines for part of the run, making them wet vents (combination vent and drain line). Nothing wrong with that as long as the wet part of the vent is below the sink or shower pan on that plumbing run. But you do need to ensure air can get in behind the water before it hits the vent, especially on the kitchen sink (air-admittance valves we talked about in your other thread). You could install an air admittance valve for the shower as well, but that's probably not needed. If you do, make sure it's higher than any other traps on that drain line.

Where do you hear gurgling? If you hear it inside the trailer in one of the sinks or shower, then the tank is not vented properly, or the vent is clogged. What's happening in that case is air is being pulled into the tank while it's draining through the only path available to it - through one or more of the traps. If you hear gurgling outside from the vent opening on the roof, then you have water trapped inside the vent line. In this case, what you're hearing is air being pulled through the trapped water in the vent while the tank is draining. That could be caused by a low spot in the tank vent that's allowing water to collect.

Chris
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Old 01-15-2014, 04:45 PM   #6
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I would like to add that Inca helped me out again. I changed my mind and decided to drain bathroom sink water into my black tank to better utilize my tank space. I needed another rubber grommet seal. I called Bill, and he had them on UPS that afternoon. I got the seals today. Bill also said the grommet hole I drill into the tanks is 2 3/16 for the grommets and 3 1/4 for the toilet flange seal. Helpful information for me. I'm using grommets instead of spin welds.

David
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Old 01-15-2014, 08:10 PM   #7
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Will the grommets provide a better seal? I am just getting to the tank phase.

Thanks
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Old 01-16-2014, 08:16 AM   #8
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Waste Tank Inlet Grommet Seal

Here are a couple of photos of the rubber grommet seals I will use on my new Inca Plastics waste water tanks. Inca provides these grommets to their RV customers. Inca recommended them to me. I don't know if Airstream uses them.

I worked in a rotomolding shop for 4 years. We used these type of rubber grommet seals for diesel and hydraulic tanks used in commercial equipment. They are reliable and seal great. And so easy to use.

Polyethylene tanks are very smooth and flat on the inside as the plastic is melted during the molding process. The grommet seals on the smooth inside surface. There is a molded rubber lip on the bottom inside diameter of the grommet. When you insert the drain pipe, the lip forces the grommet to clamp tight.

So I run my drain lines to the spot on the floor over the waste tank. I then use a hole saw and drill the clearance hole through the floor. Then I mark the location of pipe entry on the waste tank. Then I use the correct hole saw 2 3/16 diameter and drill a hole in my new tank. I deburr the hole thoroughly, and insert the rubber grommet so it seats in its groove. Finally I lubricate the grommet, and insert the pipe to a depth below the rubber lip, about 1/12 inch. The cut off of the plastic pipe must also be deburred and nice and smooth.

The grommets on my tanks are on the top surface. They will see splash water, not head pressure like the bottom of the tank sees. Most of our dump valve pipes are caulked into the 3" outlet and held tight with a hose clamp. I never thought that was a robust sealing method.

David
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Old 01-16-2014, 04:03 PM   #9
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Thanks. Now I understand.
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