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We recently made a second trip in our motorhome. I discovered that the bathroom sink is draining into the black tank. The way I discovered this was running water into the gray tank before I emptied the black tank. When I flushed the commode it ran over. I had read about this happening years ago in the trailer life magazine. I contacted the manufacturer and they said the RVIA allowed them to run one gray water line into the black water tank as long as it wasn't the shower. Has anyone else had this happen to them? ccmsm

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We recently made a second trip in our motorhome. I discovered that the bathroom sink is draining into the black tank. The way I discovered this was running water into the gray tank before I emptied the black tank. When I flushed the commode it ran over. I had read about this happening years ago in the trailer life magazine. I contacted the manufacturer and they said the RVIA allowed them to run one gray water line into the black water tank as long as it wasn't the shower. Has anyone else had this happen to them? ccmsm

Actually, there IS some merit to the sink draining into the black tank. Certainly it was done to simplify plumbing. And most of us fill the gray tank a LOT faster than the black. So you could actually dry camp longer with that arrangement unless the black tank is a lot smaller. It also doesn't hurt to add more water (vs solids) to the black tank-- makes draining easier.

How long did it take you to fill the black tank?

Brett Wolfe

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It only took a couple of days to fill it. We camped for 10 years in a 26' travel trailer. We could go 4 or 5 days without draining the black tank. The bathroom sink is straight in line with the commode so i guess it was simple for them to plumb it this way. I just wish I had known this. We love the motorhome and would have still bought it but it would have saved a mess if I had known to look out for this. ccmsm

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The tanks are 45 gallons each with a 75-gallon fresh water tank. It is a 2008 38' Georgetown motorhome. I would like for info like that to show up on my post like yours and other members but I haven't figured out how yet. I really appreciate all the info I get from this forum. Thanks to all who share their knowledge. ccmsm

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The tanks are 45 gallons each with a 75 gallon fresh water tank. It is a 2008 38' Georgetown motorhome. I would like for info like that to show up on my post like yours and other members but I haven't figured out how yet. I really appreciate all the info I get from this forum. Thanks to all who share their knowledge. ccmsm

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The tanks are 45 gallons each with a 75-gallon fresh water tank. It is a 2008 38' Georgetown motorhome. I would like for info like that to show up on my post like yours and other members but I haven't figured out how yet. I really appreciate all the info I get from this forum. Thanks to all who share their knowledge. ccmsm

Again, I am a little surprised that the toilet plus bathroom sink fills its 45 gallon tank faster than the shower and kitchen sink fill their 45 gallon tank.

Normally that small a gray tank fills very quickly. For comparison, our coach has 88 gallons potable, 40 black and 85 gray. Black is toilet only. It means that I KNOW I will not overflow black or gray while dry camping before running out of potable water.

Said another way, with those small black and gray tanks, the toilet plus bathroom sink on one and shower and kitchen sink on the other is better balanced than toilet alone on black and everything else on the other.

If this becomes an issue for you, see if you have room for a larger tank.

Brett Wolfe

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I really appreciate your input Brett. We never intend to dry camp. It is good to know we can for a couple of days if we need to. The only time I put water in the gray tank is to flush the line after emptying the black tank. Looks like I'll be doing that more often. Thanks again, ccmsm

If you truly do not use the gray tank (no showers or dish washing), then you may have some options based on how your gray and black tanks combine at the drain AND IF BOTH TANKS ARE AT THE SAME LEVEL IN THE COACH.

If both have tank valves are plumbed into a single sewer hose bib, it may be that you could install another valve downstream of the black and gray valves but upstream of where the sewer hose attaches. Leave this new valve closed. Open the two upstream valves. Now both tanks share in your "usable capacity" of 35 plus 35 gallons. Most actually use more shower plus kitchen sink than toilet plus head sink, but it really doesn't matter. If another arrangement works better for you, GO FOR IT.

Again, your coach's tank placement (side by side vs one on top of the other) and valve arrangement will determine if this could work for you.

Brett Wolfe

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That brings up another question. I have always connected to the campground sewer when we get there and leave the gray water line open till I need to empty the black tank. Is this not good?

Many follow the same practice-- leave gray open to drain and only drain black when 3/4 or more full.

A slight improvement IF gray and black share the same sewer hose is to leave both valves closed. Drain black first. Then raise the sewer hose (now empty) to tank level and with the black valve still open, open the gray valve. What you are doing is sending a massive rush of water from gray to black. That helps dislodge any solids. As soon as you hear the rush of water subside, just lower the hose and let it drain as always.

And always put a couple of gallons of water through the toilet with the valves open and then after closed a couple more gallons.

Obviously, if you are going through a lot of gray (wash machine, etc) leave the gray open.

Brett Wolfe

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