Gray tank drain size

[davidmurphy02]

Sitting around in quarantine my mind has been wandering to some wishful thinking items. One minor annoyance has always been the relatively slow draining of the gray tank because of the smaller diameter drain pipe. On our 5.0TA the black tank empties in less than ten seconds, while the gray tank seems to take forever while I stand there twiddling my thumbs at the dump station. If I could design my perfect trailer I think I'd put a 3" drain pipe and gate valve on the gray tank just like the black tank has.

The biggest reason I can see for the RV industry using a smaller drain pipe for gray is to make the distinction between the two very obvious - with two identical drain pipes and gate valves someone could get them confused and open the wrong valve, getting black water when they were expecting gray.

Seems like it would be easy to put a different handle on the gray gate valve - in fact, on my trailer the 1-1/2" gray valve handle is a light gray color. Just wondering if anyone else has ever thought of doing this, and whether there were potential drawbacks that I am missing. And there may be an RV industry code requiring the smaller size drain on the gray tank which would make this a moot point.

Can you tell I'm a little bored today?

[tdf-texas]

Originally Posted by davidmurphy02

Sitting around in quarantine my mind has been wandering to some wishful thinking items. One minor annoyance has always been the relatively slow draining of the gray tank because of the smaller diameter drain pipe. On our 5.0TA the black tank empties in less than ten seconds, while the gray tank seems to take forever while I stand there twiddling my thumbs at the dump station. If I could design my perfect trailer I think I'd put a 3" drain pipe and gate valve on the gray tank just like the black tank has.

The biggest reason I can see for the RV industry using a smaller drain pipe for gray is to make the distinction between the two very obvious - with two identical drain pipes and gate valves someone could get them confused and open the wrong valve, getting black water when they were expecting gray.

Seems like it would be easy to put a different handle on the gray gate valve - in fact, on my trailer the 1-1/2" gray valve handle is a light gray color. Just wondering if anyone else has ever thought of doing this, and whether there were potential drawbacks that I am missing. And there may be an RV industry code requiring the smaller size drain on the gray tank which would make this a moot point.

Can you tell I'm a little bored today?

I didn't replace the outlet fitting on the tank but I did increase the drain piping size to 2".

https://www.escapeforum.org/forums/f...tml#post240325

https://www.escapeforum.org/forums/f...tml#post275426

With correcting the piping slope issue and increasing the pipe size, grey tank drainage is much faster.

[Ian and Sue]

Originally Posted by davidmurphy02

Sitting around in quarantine my mind has been wandering to some wishful thinking items. One minor annoyance has always been the relatively slow draining of the gray tank because of the smaller diameter drain pipe. On our 5.0TA the black tank empties in less than ten seconds, while the gray tank seems to take forever while I stand there twiddling my thumbs at the dump station. If I could design my perfect trailer I think I'd put a 3" drain pipe and gate valve on the gray tank just like the black tank has.

The biggest reason I can see for the RV industry using a smaller drain pipe for gray is to make the distinction between the two very obvious - with two identical drain pipes and gate valves someone could get them confused and open the wrong valve, getting black water when they were expecting gray.

Seems like it would be easy to put a different handle on the gray gate valve - in fact, on my trailer the 1-1/2" gray valve handle is a light gray color. Just wondering if anyone else has ever thought of doing this, and whether there were potential drawbacks that I am missing. And there may be an RV industry code requiring the smaller size drain on the gray tank which would make this a moot point.

Can you tell I'm a little bored today?

Most of the volume of the tank drains fairly quickly. I do not know how much is left when it starts to slow down but it seems like it is not much...why worry, go camping! If it is really important get to where you are going and put a 5 gal bucket under it and let it drain, then dump the bucket in the nearest sink. I might get a couple of gallons this way tops.

[padlin]

I stopped mine one time as soon as it started to trickle off, after something like a minute or so of starting to dump. Restarted draining with a bucket under it. Took about 5 minutes and got 2 1/2 gallons more, out of 29. I no longer wait for it to finish, when it slows way down I call it done.

[rubicon327]

Originally Posted by davidmurphy02

Sitting around in quarantine my mind has been wandering to some wishful thinking items. One minor annoyance has always been the relatively slow draining of the gray tank because of the smaller diameter drain pipe. On our 5.0TA the black tank empties in less than ten seconds, while the gray tank seems to take forever while I stand there twiddling my thumbs at the dump station. If I could design my perfect trailer I think I'd put a 3" drain pipe and gate valve on the gray tank just like the black tank has.

The biggest reason I can see for the RV industry using a smaller drain pipe for gray is to make the distinction between the two very obvious - with two identical drain pipes and gate valves someone could get them confused and open the wrong valve, getting black water when they were expecting gray.

Seems like it would be easy to put a different handle on the gray gate valve - in fact, on my trailer the 1-1/2" gray valve handle is a light gray color. Just wondering if anyone else has ever thought of doing this, and whether there were potential drawbacks that I am missing. And there may be an RV industry code requiring the smaller size drain on the gray tank which would make this a moot point.

David: I think the only reason the black line is a bigger diameter is because it has to pass solids. The line is a bit large to drop beneath the frame rail so that is why it drops down from the shell outside the frame. The gray is a bit small at 1.5” but it makes it easier to route the plumbing. I followed Tom’s lead and installed a Valterra T84 with two 3” valves and upsized the gray line to 2”. Definitely better draining. One advantage is you only need to carry one size spare valve and I got a better pitch on the gray line with the use of an eccentric reducer fitting. See dump vallve mod thread linked above. Before any surgery though I would try a couple of tests to see if you get improvement. One test is pulling the far side up on a block to get a better pitch towards the drain. Another would be removing the shower drain stopper to see if that allows for better venting. It shouldn’t if the trap is designed properly and is full of water but with the shallow traps ETI has been known to use it likely isn’t full. If you get improved flow with one or both of these techniques then maybe you don’t even touch your valves.

[Brian B-P]

Originally Posted by davidmurphy02

One minor annoyance has always been the relatively slow draining of the gray tank because of the smaller diameter drain pipe.

You are assuming that the smaller diameter is the problem, and I don't think that's true. The black and grey systems are carrying different waste mixes, through different lengths of differently configured piping... and none of that matters much compared to the vertical drop difference. The grey tank is under the floor, so the outlet is at essentially the same level as the bottom of the tank, but the black tank is top of the floor. The black tank is much higher, so the waste has much more help from gravity.

Even if the piping from the two waste tanks were equal in diameter, length, and configuration, and both had the same waste in them, the black waste would drain much more quickly.

Originally Posted by davidmurphy02

The biggest reason I can see for the RV industry using a smaller drain pipe for gray is to make the distinction between the two very obvious - with two identical drain pipes and gate valves someone could get them confused and open the wrong valve, getting black water when they were expecting gray.

Seems like it would be easy to put a different handle on the gray gate valve - in fact, on my trailer the 1-1/2" gray valve handle is a light gray color.

The RV industry uses different sizes for black and grey waste piping for the same reason that drain/waste/vent piping in buildings comes in different sizes. Excessively large piping is more expensive, and more difficult to route. As Dave pointed out, the solids in the black tank contents require larger piping.

Originally Posted by davidmurphy02

Seems like it would be easy to put a different handle on the gray gate valve - in fact, on my trailer the 1-1/2" gray valve handle is a light gray color.

I doubt that many RV users look at the piping sizes (they remember which handle is on which side), and different handle colours seems like a reasonable way to make them easily distinguishable. Some RVs have labels for valve handles, especially RVs in which the handles come through a control panel.

[padlin]

The gray's outlet is on the side of the tank vs the black's being on the bottom, at least mine are, tipping the trailer is the only way I can see of speeding things up.

[escape artist]

Originally Posted by davidmurphy02

Sitting around in quarantine my mind has been wandering to some wishful thinking items. One minor annoyance has always been the relatively slow draining of the gray tank because of the smaller diameter drain pipe. On our 5.0TA the black tank empties in less than ten seconds, while the gray tank seems to take forever while I stand there twiddling my thumbs at the dump station. If I could design my perfect trailer I think I'd put a 3" drain pipe and gate valve on the gray tank just like the black tank has.

The biggest reason I can see for the RV industry using a smaller drain pipe for gray is to make the distinction between the two very obvious - with two identical drain pipes and gate valves someone could get them confused and open the wrong valve, getting black water when they were expecting gray.

Seems like it would be easy to put a different handle on the gray gate valve - in fact, on my trailer the 1-1/2" gray valve handle is a light gray color. Just wondering if anyone else has ever thought of doing this, and whether there were potential drawbacks that I am missing. And there may be an RV industry code requiring the smaller size drain on the gray tank which would make this a moot point.

Can you tell I'm a little bored today?

Hi: davidmurphy2... Have you tried opening the shower floor drain B/4 pulling the grey tank gatevalve? Just thinking!!! Alf
escape artist N.S. of Lake Erie

[davidmurphy02]

Originally Posted by escape artist

Hi: davidmurphy2... Have you tried opening the shower floor drain B/4 pulling the grey tank gatevalve? Just thinking!!! Alf
escape artist N.S. of Lake Erie

I have not tried that but will next time. We keep the shower drain firmly screwed shut except when using the shower because the cats' litter box resides on the bathroom floor, some litter inevitably gets kicked overboard and we sure don't want cat litter going down the drain. Next time out I will definitely try opening that drain and see if it makes a difference. Now we just need to cross our fingers and hope that the next time out isn't too far off in the distant future....

[alanmalk]

Originally Posted by escape artist

Hi: davidmurphy2... Have you tried opening the shower floor drain B/4 pulling the grey tank gatevalve? Just thinking!!! Alf
escape artist N.S. of Lake Erie

Wondering...
Isn't there a vent on the grey tank to the outside that would prevent a vacuum - with similar results that opening the shower drain would achieve?
But if opening the shower drain helps I will be jumping on that bandwagon.
--
Alan

[gbaglo]

I believe. Round, about 2" diameter. Just below the fridge vent near that sticker on my 2009 17B.