Gray Tanks Empty VERY slowly

[Bob and Kristen]

Our gray tanks seem to take forever to empty. After about 45 minutes, I finally just close the gates even though water is still trickling through. Our tanks are 2/3 full or completely full when we dump. The water gushes out fast at first but then slows to a trickle after a few minutes. We live in Michigan so I don't want to spend that long trying to get the gray tanks to empty in the Winter. We are parked on our property so I've got the time to wait but it never seems like it empties fully. I couldn't imagine trying to dump them at a campground - they have always taken this long, even when our rig was brand new. Any help as to what might be causing this will be greatly appreciated.

Thanks,
Kristen

[ThePowells]

Bob and Kristen Welcome to the family and the forum.
Our 390has the same tanks that you have. They have pronounced sags in the tanks and then when you have soap scum in the bottom of the gray tanks, that seems to hold water. I pulled my gray tank valve to reseal it and when I looked in the tank I was amazed at what was in the bottom and the sag holding water. This was even after putting the nose up 2.1 degrees and draining it and after pulling the valve and reaching inside, again was amazed and the stuff on the bottom felt like it was a sponge (Yes, I put my hand in it). When the flow drops to a small stream, you should be done. Running hot water until it gets to warm with a mega dose of Dawn and Borax the travel agitation may help break up the bottom crud.

I see that y'all are new here and and this was put together and may help you navigate the forum. https://gdrvowners.com/forum/main-fo...to-new-members

[Cate&Rob]

Bob and Kristen ThePowells

Hi Kristen,

I think Jerry has answered your question correctly, but I thought I might add a couple of pictures to explain this further. The gate valves that drain the grey or black tanks are attached to the ends or sides of the tanks. The gate opening is inside a flange that leaves the low point of this drain significantly above the bottom of the tank. This means that this drain point will never allow the tank to completely drain. There will always be something like 1/2" of water & sediment in the bottom of the tank. This pool will continue to "dribble" out the gate valve opening for a long time (as you have experienced) after the tank has drained down to this point.

Rob

[ThePowells]

Bob and Kristen I'll expand a bit on what Cate&Rob posted. When I posted this morning, I didn't have access to my photos. Hopefully this will help put things into perspective. You can see where the bottom edge of the valve is and where the bottom of the tank actually slopes away from the valve.

[Bob and Kristen]

Thanks Jerry and Rob! You both have helped save me 40 minutes every week. I appreciate the pictures because that always helps to see what is actually happening behind the curtain.

[RJAPCOK]

I want to say that this thread has been very helpful to me, even though I wasn't the one who asked the question. Quite by accident, I discovered that my tanks did not seem to be emptying completely. My workaround was to drive up on blocks on the off side, so that the drain valve side was lower when I dumped them. That helped them to drain more completely. But this thread and the attached photos helped me to understand the problem.

Thanks you!
Bob