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Gray Tank Drains Slow

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The gray tank in our 2006 Dolphin drains slow. Fast at first and slows down to a trickle, i can hear the liquid draining into the drain hose. Gray tank take about 20 minute to drain. What can I put in the tank to get rid of any sludge that could be blocking half if the drain?

Bob

RWDMLD18

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Bob,

Before you resort to chemicals that could harm the valves or plastic, tanks and lines, use a hose with regular garden nozzle. Start from each gray water INLET (both sinks, shower, etc). Flush with plenty of city water pressure.

If it is still trickling out, after the tank is empty, put a bucket/storage container under the drain where you attach the hose. Lining it with a garbage bag will keep the bucket/storage container clean. Shoot the water pressure up the outlet toward the valve.

If it still doesn't come out as it should, I would remove the valve and make sure it is working properly.

Cleanest way to do that is to use your leveling jacks (or boards if you don't have jacks) to lean the coach with the drain side lower. Let the tank drain completely. Use the jacks/boards to lean the coach the OTHER way, so nothing will try to drain out of the tanks when you remove the valve.

Now remove the valve. I use pure silicone GREASE (not sealer) on the valve seals. Makes them easy to open and close for a whole season. The valves are not that expensive-- it one does not free up, replace it. I always carry a spare valve in my parts kit.

Brett

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Has this always been the case or is this a new development? How long does the fast flow last? If it is just a momentary gush and then a trickle, it might be a fixed obstruction where the drain pipe exits the tank. If the fast flow lasts for something like a minute or two then slows suddenly, it could be something loose in the tank which is washing around in the tank when it is full but then drawn to the drain when the tank is emptied. That could be a rag or a loose piece from a tank cut out.

In either case, it doesn't sound like a sludge problem. Sludge should be washed out by the fast flow unless you have one heck of a hairball! There are tank treatments that will reduce buildup in a tank. These usually function best if left to set in the tank when near full and then emptied after driving to stir the tank thoroughly. Check any RV store for cleaners, Thetford makes several variates. I've heard some people recommend using a septic tank cleaner which could be found at any hardware store.

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Hi Bob,

Because the tank drains fast at first then slows to a trickle, it sounds like there is something in the tank that floats or is light enough to move around when the coach is driven and the tank is being filled. The item is then drawn to the tank drain location. Gut feel says the item is remaining in the tank and not flowing into the train pipe. If this ends up being the case, consider taking the coach to a RV shop. Depending on the location of the tank drain the drain pipe may need to be removed.

I know of no chemicals that will dissolve something that is stuck in the grey tank without creating other problems with the valve and seals.

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