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Old 12-30-2020, 02:45 PM   #1
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Model: Challenger 37FH
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THOR #20476
Rear bath sink drain

I have a Challenger 37fh (with the 1 1/2 baths) (2 black tanks and 2 grey tanks). The sink in the rear bath drains into the black tank rather than the grey water tank. This causes the black tank to fill quicker and when boon-docking limits the time til black tank needs dumped. To minimize the effects we just do not use that sink when boondocking.

Has anyone redirected this sink drain to the grey water tank? If so, how did this modification work?

I am thinking of adding a y-valve to direct this water to the grey tank or just permanently changing the drain line to the grey water tank.

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Old 12-30-2020, 03:45 PM   #2
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We have a Challenger 37LX. Bath and a half, with dual black and dual grey tanks like yours. I find that my grey tanks fill up way before my black tanks do. We have gone 10 days before dumping the black tanks, and even then I don’t think they were completely full.

It is just my wife and myself, so if you have more people on board that might explain why yours are filling so fast.

I’m actually glad that the lavatory sinks empty into the black rather that the grey tanks.
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Old 12-30-2020, 05:16 PM   #3
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FYI...
there's a reason why all RVs drain the bath sink into the Black tank
it's to add a little soapy sink water to the solids

personally, I would not change it
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Old 12-30-2020, 07:38 PM   #4
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Quote:
Originally Posted by ptylerp View Post
I have a Challenger 37fh (with the 1 1/2 baths) (2 black tanks and 2 grey tanks). The sink in the rear bath drains into the black tank rather than the grey water tank. This causes the black tank to fill quicker and when boon-docking limits the time til black tank needs dumped. To minimize the effects we just do not use that sink when boondocking.

Has anyone redirected this sink drain to the grey water tank? If so, how did this modification work?

I am thinking of adding a y-valve to direct this water to the grey tank or just permanently changing the drain line to the grey water tank.
you probably have rear axels to jump over and we all know which way that runs.
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Old 12-30-2020, 08:03 PM   #5
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Originally Posted by taylorbob1 View Post
FYI...

there's a reason why all RVs drain the bath sink into the Black tank

it's to add a little soapy sink water to the solids



personally, I would not change it


They don’t “all” drain into the black tank. Some do and some don’t. If you want to know either get a diagram from the manufacturer or, after draining the grey and black tanks run the bathroom sink faucet for a few minutes and see which tank it comes out of.
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Old 12-31-2020, 04:29 PM   #6
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Taylorbob1 is right it helps draining black tank we've also have 37fh and always fill rear gray from showers well before black, both tanks are 40 gallons.
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Old 12-31-2020, 06:55 PM   #7
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I don't know if we've had this question before.
If we haven't, a slight change in personal habits might be the answer.

Also:
If you have a hard pipe over the axle I think a $18 water flow sensor, a $78 macerator pump and a garden hose would make me a lot less worried about some wonky ridgid line in a really stupid place.
And
My rv has room for two more tanks, another 100gallons+-underneath.
A 40 gallon tank is about $140....

I considered it and measured for it.
It turns out we don't have the need.
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Old 01-05-2021, 09:16 PM   #8
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I just checked the schematics for my 2018 Vegas 24.1 and the bathroom sink and kitchen sink and shower drains to the grey tank. The toilet is the only item that drains to the black.
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Old 01-05-2021, 09:39 PM   #9
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Originally Posted by gte534j View Post
I just checked the schematics for my 2018 Vegas 24.1 and the bathroom sink and kitchen sink and shower drains to the grey tank. The toilet is the only item that drains to the black.
Those schematics are not 100% accurate. When we got the Gemini I was trying to figure out why the black tank filled so quickly. The schematic clearly showed both the kitchen and bathroom sinks draining into the grey tank. A physical inspection clearly showed the drain line from the bathroom sink going directly into the black tank. I just learned to live with it, used the bathroom sink very judiciously.
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Old 01-09-2021, 08:55 PM   #10
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Black water vent

The reason that they use the bathroom sink for the black tank, is that they both need roof vents. The blackwater vent passes near the sink, thus giving them both a common roof vent.
If you separate the drains, you will need to vent whichever now does not have a vent.
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Old 01-09-2021, 10:41 PM   #11
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Originally Posted by davidspixx View Post
The reason that they use the bathroom sink for the black tank, is that they both need roof vents. The blackwater vent passes near the sink, thus giving them both a common roof vent.
If you separate the drains, you will need to vent whichever now does not have a vent.


My bathroom sink uses a studervent under the sink and drains into the grey water tank. Same as the kitchen.
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Old 01-09-2021, 11:36 PM   #12
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When the bathroom sink drains to the black water tank, is it probable that the adjacent shower also drains to the black water tank, instead of the grey water tank? The head is located between the sink and the shower in a dry bathroom.
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Old 01-10-2021, 12:32 AM   #13
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Originally Posted by davidspixx View Post
The reason that they use the bathroom sink for the black tank, is that they both need roof vents. The blackwater vent passes near the sink, thus giving them both a common roof vent.
If you separate the drains, you will need to vent whichever now does not have a vent.
Ummmm, no. You only need a roof vent for each tank. Sinks normally have Air Admittance Valves (AAV) these days.
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Old 01-10-2021, 12:42 AM   #14
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Hi ptylerp

The reason why the bathroom sink drains into the black tank is to add additional water to the black tank to help move all solids out when you do a dump. The black tank usually needs a little more water to help move everything out and not leave solids to build up. Your kitchen sink and shower usually go into the grey tank.

Paul
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Old 04-03-2021, 05:50 AM   #15
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Originally Posted by paulwadley View Post
Hi ptylerp

The reason why the bathroom sink drains into the black tank is to add additional water to the black tank to help move all solids out when you do a dump. The black tank usually needs a little more water to help move everything out and not leave solids to build up. Your kitchen sink and shower usually go into the grey tank.

Paul
'

This is what they also told us when we asked at the RV place. We just have the two of us so we just don't use the bathroom sink. I add a bit of water just to keep the pee trap full, or when I want to fill the black tank a bit quicker for flushing the black tank.
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Old 04-03-2021, 02:02 PM   #16
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On mine (SOB) the bathroom sink drain into the gray tank. I wish it went to the black. Our gray tank always fills up much faster than the black.
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Old 04-03-2021, 03:27 PM   #17
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Originally Posted by taylorbob1 View Post
FYI...
there's a reason why all RVs drain the bath sink into the Black tank
it's to add a little soapy sink water to the solids

personally, I would not change it
Has nothing to do with adding soapy water to the solids. Soapy water is not needed by the black tank.
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Old 04-03-2021, 03:29 PM   #18
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Originally Posted by Pete'sMH View Post
On mine (SOB) the bathroom sink drain into the gray tank. I wish it went to the black. Our gray tank always fills up much faster than the black.
Same on my rig. On the prior rig (Challenger) only the toilet went to the black tank. The shower and outdoor kitchen went to the rear grey tank and the kitchen and bathroom sinks went to the forward grey tank.
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Old 04-03-2021, 03:49 PM   #19
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The biggest reason the lavatory drains into the black tank is LOCATION. If the toilet & sink are in the rear with the kitchen & other bath is in the front it's not feasible to run the sink drain to the other grey tanks bypassing the easy connection. ALL rv toilets should dump fairly straight down into the black tank so they should be directly over the tank, if the sink is next to the toilet there's probably no where to run a line to a grey tank from the sink + the extra liquid helps break down & drain the solids & paper. If you're filling the black tank quickly by only running the bath sink someone's running a lot of water to wash their hands & brush their teeth, if the shower also drains into the black that's a different story.
The manufacturer doesn't do this just to inconvenience the buyer, it's easier & less expensive to do it this way depending on floorplans.
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Old 04-03-2021, 04:24 PM   #20
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Originally Posted by Travelin' Texans View Post
The biggest reason the lavatory drains into the black tank is LOCATION. If the toilet & sink are in the rear with the kitchen & other bath is in the front it's not feasible to run the sink drain to the other grey tanks bypassing the easy connection. ALL rv toilets should dump fairly straight down into the black tank so they should be directly over the tank, if the sink is next to the toilet there's probably no where to run a line to a grey tank from the sink + the extra liquid helps break down & drain the solids & paper. If you're filling the black tank quickly by only running the bath sink someone's running a lot of water to wash their hands & brush their teeth, if the shower also drains into the black that's a different story.
The manufacturer doesn't do this just to inconvenience the buyer, it's easier & less expensive to do it this way depending on floorplans.
You are correct. The Challenger was based on left and right and not front and rear. The shower and outdoor kitchen were on the passenger side and the kitchen and bathroom sinks were on the drivers side.
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