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Old 08-21-2021, 06:58 PM   #1
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Connecting Garden Hose to Black Tank Flush Connection

What am I missing here? So I've used my dedicated 15' hose a hundred times...attaching it to this connection and tightening it perfectly. This last time I could not get it to tightly connect and it spewed like a hose at a water park. I inspected the edge and determined that it looked like the brass connection on my hose was out-of-round...no problem, right, I'll just replace this hose.

So after my Lowe's run, I find that the new hose does not thread on any better and I thought it was basically identical to my previous one. Does anyone know if this black tank flush connection requires a larger hose size such as 1/2" or 3/4" to fit properly? (I'm in a Forester MH Model 2801.) It is possible I purchased a 3/8" which obviously wouldn't fit. Thanks for the input!
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Old 08-21-2021, 07:07 PM   #2
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Update: My new hose is 5/8" and connects to my old hose fitting just fine.
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Old 08-21-2021, 07:33 PM   #3
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Black tank flush fitting should fit any regular garden hose, whether it be a 1/2" or 5/8". Just have to make sure the rubber gasket in the camper side fitting is good.

Oh, see you got it. Glad it worked out.
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Old 08-21-2021, 07:55 PM   #4
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No the new 5/8" size hose did not really fit. The brass fitting seems to fit way up into the black valve hose fitting and I can barely get a thread or two to catch when tightening. The plastic valve fitting threads do not seem like they are stripped...just a larger connection than a standard 5/8" fitting. I'm baffled!
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Old 08-21-2021, 08:03 PM   #5
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The hose connection is a 3/4" "garden hose" type. The 1/2", 5/8" or 3/4" is the interior size of the actual hose, but the connectors should all be standard. Larger inner diameter hose will flow more water, but for the short distance and RV usage 1/2" is plenty. It's when you want to run a big sprinkler 150' from the faucet and put down a ton of water on the lawn that 3/4" makes a difference.

It sounds like the female adapter on the trailer for black flush may be going bad. First thing is to check and make sure there is a washer inside that fitting. No washer will spray like that every time. You can get replacement washers for next to nothing at any hardware store and probably even the grocery store or dollar store.

The hose washer/gasket should look like this, but it may not be black. It should be inside the fitting ON THE TRAILER (the female connector):



I've been replacing all my rubber hose washers with silicone ones. They don't tend to harden and crack like rubber does. So far it's working great. I got a pack of 20 on Amazon for like $6 a while back.
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Old 08-21-2021, 08:03 PM   #6
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Quote:
Originally Posted by ArkRVHog View Post
No the new 5/8" size hose did not really fit. The brass fitting seems to fit way up into the black valve hose fitting and I can barely get a thread or two to catch when tightening. The plastic valve fitting threads do not seem like they are stripped...just a larger connection than a standard 5/8" fitting. I'm baffled!
The 5/8 is just the size of the rubber hose diameter. The connections on a 5/8 hose and a 1/2 hose are the same size. Just more water will flow thru the bigger hose.

Make sure the gasket inside the female connection to black tank is seated all the way back. Sounds like the gasket has maybe moved forward.
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Old 08-21-2021, 09:55 PM   #7
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Originally Posted by dward51 View Post
The hose connection is a 3/4" "garden hose" type. The 1/2", 5/8" or 3/4" is the interior size of the actual hose, but the connectors should all be standard. Larger inner diameter hose will flow more water, but for the short distance and RV usage 1/2" is plenty. It's when you want to run a big sprinkler 150' from the faucet and put down a ton of water on the lawn that 3/4" makes a difference.

It sounds like the female adapter on the trailer for black flush may be going bad. First thing is to check and make sure there is a washer inside that fitting. No washer will spray like that every time. You can get replacement washers for next to nothing at any hardware store and probably even the grocery store or dollar store.

The hose washer/gasket should look like this, but it may not be black. It should be inside the fitting ON THE TRAILER (the female connector):



I've been replacing all my rubber hose washers with silicone ones. They don't tend to harden and crack like rubber does. So far it's working great. I got a pack of 20 on Amazon for like $6 a while back.
Great explanation of garden hose sizes (I should have known that) and the nice photo showing the washer/gasket! The connection does have a gasket in it, even with a little debris screen. I've taken it out and inspected it for wear...it looks fine. Another poster made a good point of being sure it is not only present but seated to the back of the fitting...it is.

I just can't figure out why a fitting (the black tank female side) has all of a sudden become somewhat larger than the male hose fitting (or seems that way) that has always fit just fine? Should I make an appointment with a marriage counselor about this....wink.

It will cost me about $20 to order a new B&B Water flange...I might try that next. https://smile.amazon.com/gp/cart/vie...?ref_=nav_cart
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Old 08-21-2021, 10:29 PM   #8
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Put quick connect fittings on the hose and the flush fitting. Takes about two seconds to hook up using one hand.
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Old 08-21-2021, 10:33 PM   #9
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Ops Iím baffled and interested pics would be greatÖ
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Old 08-22-2021, 08:55 AM   #10
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Two seconds was for a two handed hookup. One hand is closer to five seconds. You only have to screw the fitting in once.

https://imgur.com/Bv49CEz.mp4
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Old 08-22-2021, 09:20 AM   #11
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If you have a wet bay install this 90ļ elbow/connect 1/2" coiled hose and don't disconnect/store coiled hose in wet bay.
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Old 08-22-2021, 10:10 AM   #12
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I always use 90 degree fittings on all my hook ups. It takes the strain off the fitting of a heavy hose hanging straight out from the plastic fittings.
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Old 08-22-2021, 10:33 AM   #13
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Exclamation

Male and female hose fittings are universal. They are all the same size - 3/4s of an inch - with the same threading. I would remove that washer with the screen and replace it with a normal washer, either rubber or silicone. Make sure it is seated all the way into the female fitting. When you attach the hose, make sure you tighten the fitting by hand as tight as possible. If it still leaks, I have to assume that the threads on the female fitting are defective, and the fitting should be replaced.
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Old 08-22-2021, 01:23 PM   #14
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Male and female hose fittings are universal. They are all the same size - 3/4s of an inch - with the same threading. I would remove that washer with the screen and replace it with a normal washer, either rubber or silicone. Make sure it is seated all the way into the female fitting. When you attach the hose, make sure you tighten the fitting by hand as tight as possible. If it still leaks, I have to assume that the threads on the female fitting are defective, and the fitting should be replaced.
2X Remove washer with screen. I also spray Pam cooking spray on all my hose rubber washers as a lubricant and it is food safe. Been doing that for years.
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Old 08-22-2021, 01:38 PM   #15
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mine came with a threaded adapter ,screws on trailer then hose ,plastic , no more crazy spray .
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Old 08-22-2021, 01:47 PM   #16
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I have experienced a similar problem with 1/4 turn plastic inline garden hose shutoff valves. The shutoff valves (made in China) fit the majority of my hoses and fittings with one exception. The male end of my fresh water fill hose only screws on to the valve a couple of turns. It feels like it is seated against the washer, however when turned on it leaks badly. My solution was to tighten the connection with pliers (at the risk of cracking the plastic). It has been leak free for several months and I just keep the valve "permanently" installed on the hose.
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Old 08-22-2021, 02:17 PM   #17
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This thread seems to be branching into more than one direction. But, that's not all bad as they're all related.

I'm in total agreement with the prior points:
  1. Try to avoid screwing metal into existing plastic; odds are that eventually plastic treads on the RV will be stripped. A 90 deg. brass adapter solves that problem - install it once and leave it on.
  2. Quick disconnects are another way, and make for fast connections, especially when others are waiting for you to complete your work. A QD into the 90 works well for me. I use on both my FW and BTF ports and on my respective hoses.
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Old 08-22-2021, 04:38 PM   #18
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have you tried Teflon tape
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Old 08-22-2021, 04:59 PM   #19
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Originally Posted by emm-dee View Post
Put quick connect fittings on the hose and the flush fitting. Takes about two seconds to hook up using one hand.
The US garden hose thread size is 3/4-inch GHT with 11.5 tpi; also known as NHR or MHT. They've been that way for well over a hundred years. If the OP can not get his current hose or new garden hose to seal, I suspect that the blank tank flush fitting is either tweaked (out-of -round), or cross-threaded somewhere. Chances are the QD fitting isn't going to seal, either.
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Old 08-22-2021, 05:29 PM   #20
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Two washers

Sometimes you simply have to use two washers. One good example is where there is a backflow preventer on the tap at the pedestal. The threaded stub on the MGH (Male Garden Hose) end of the backflow preventer is very short. The threaded FGH (Female Garden Hose) connector will butt up against the body of the backflow preventer before the washer is compressed. Stacking two washers into the FGH connector solves that problem.
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