Northpoint grey tank drain

[Lake Huron]

I got 5 tanks, 2 black, 3 grey. The front drain has the front black and front grey that the shower, and vanity dump into along with the washer prep which we've never used. The black tank is on the right side of the trailer that hits the main drain line, passes by the grey tank wye fitting and two 90* turns later is out the left side of the trailer. I have a clear 45* fitting that attaches to my sewer hose so I can see what and how much is coming down the pipe. When I dump the black tank the entire clear 45 is filled. When I dump the grey, no matter if the tank is completely full or half, it doesn't come rushing out as fast. About half the clear 45 is filled. It seems like it takes FOREVER to drain it. The first few times we used it when it was brand new it didn't seem to be this slow. The rear grey tanks will scream liquid out of them. I took the back basement wall down and took a look around in there. It seems like the valve cable is fully opening and closing. I took it out and lube it up a little bit and readjust the cable to make sure it is fully opening and closing. I had a plumber run a camera up the sewer line but we couldn't see up into the grey wye or valve to see if there is a blockage or anything. I also checked for venting. If the tank was full it would gurgle to get air back into the tank. I also put a leaf blower up to the sewer outlet with the grey tank valve open and could feel a LOT of air coming out the vent stack on the roof. The one thing I did notice was the size of the grey tank valve. The sewer line is a 4". The black tank valve is a 4". The outlet on the grey tank is a 4" but has a reducer coupler on it and the valve is a 1 1/4" that goes to a 1 1/4" on the wye end.
Can someone please tell me why they did this instead of making it a 4" all the way??

[Jagiven]

Good question. As long as I can remember the black is a 4" pipe,and the grey is much smaller. I was thinking 1.5". I really wish it to was 4". I would think it would do a better job rinsing out the sewer hose.

[Grumpy]

Originally Posted by Lake Huron

Can someone please tell me why they did this instead of making it a 4" all the way??

Common in the RV industry. It's called lower cost.....

[Stevek10]

I have the opposite as you, the grey dumps fast and the black is slow, and always has been. I've listened as the macerator pump surges as it waits for more liquid to pump. It's quite frustrating because I want the higher flow to get everything flushed out of the tank. The only think I can think is the vent. The grey and the black vents merge somewhere behind the wall in the bathroom before coming out the roof. I cant tell if the tee is obstructed and that's what's limiting the flow. My guess is poor workmanship judging how the pipes are run in the void space that I can see.

[AKRUEBBE]

Originally Posted by Stevek10

I have the opposite as you, the grey dumps fast and the black is slow, and always has been. I've listened as the macerator pump surges as it waits for more liquid to pump. It's quite frustrating because I want the higher flow to get everything flushed out of the tank. The only think I can think is the vent. The grey and the black vents merge somewhere behind the wall in the bathroom before coming out the roof. I cant tell if the tee is obstructed and that's what's limiting the flow. My guess is poor workmanship judging how the pipes are run in the void space that I can see.

Have you tried waiting about a minute after you pull the black valve to turn the maerator on? I don't have a problem with my black tank being slow, but the bathroom grey tank is and I find if I wait a minute before turning the macerator on it helps give a continuous flow.

[Stevek10]

Originally Posted by AKRUEBBE

Have you tried waiting about a minute after you pull the black valve to turn the maerator on? I don't have a problem with my black tank being slow, but the bathroom grey tank is and I find if I wait a minute before turning the macerator on it helps give a continuous flow.

Unfortunately its throughout the entire dump, even when I'm using the sewer hose, just surges instead of stready.

[Donna]

We have NP 351RSQS and have pretty much same issue with grey tank side. Haven't investigated much, but somebody was telling me that maybe extending the vent caps up top may help.

[AKRUEBBE]

My #1 grey tank valve doesn't seem to be opening all the way. I feel some initial resistance but then no resistance when pulling the valve all the way. Can the valve be accessed from behind the water control panel to check if the valve arm is fully opening?

[Stevek10]

Originally Posted by AKRUEBBE

My #1 grey tank valve doesn't seem to be opening all the way. I feel some initial resistance but then no resistance when pulling the valve all the way. Can the valve be accessed from behind the water control panel to check if the valve arm is fully opening?

Remove the big panel with the vacuum in it to get to grey tank valve. Tanks is toward the kitchen.

[AKRUEBBE]

Originally Posted by Stevek10

Remove the big panel with the vacuum in it to get to grey tank valve. Tanks is toward the kitchen.

Are you saying that the valve is all the way on the passenger side of the TT?!

[Stevek10]

Originally Posted by AKRUEBBE

Are you saying that the valve is all the way on the passenger side of the TT?!

It's dead center