Black water flush line - winterizing??

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Wagonmaster2

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May 2, 2009
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I hope this is Winnebago specific but here's my question.  Is it possible for any water to remain in the black water flush line even after leaving the cap off where the water hose connects to for the flushing?  I've been winterizing my 2004 Meridian 36G for 8 years without doing anything special with this line but one of the Posters on another Forum stated his line had frozen because he either didn't blow it out or pink it.

Does this line continually slope upwards to the tank so there's no possible way for water to remain in it, and where does it connect to the black tank, top or side?  Is there a valve or something like that in this line to keep sewage from draining down into it if the black tank were to get completely full?  Which I try to always avoid but when dry camping for over a week it can get pretty full.

I tried yesterday to find my blow-out-plug, which I know I have but since I very seldom use it I couldn't remember where I had seen it last.  One RV shop was out of them and the other was closed till after Christmas.  Waited too long I guess.

Since I've never done anything with it in the past I can't get too concerned but once you start thinking about something it's hard to get it out of your mind.  Shouldn't be too hard for me though since there's so little room in there a person would think it would just fall out.

MERRY CHRISTMAS ALL !!
 
There is definately a check valve in the line. Mine stuck closed once, and last week was stuck open when I started to dump a very full tank and opened it up to hook up the hose!  :eek:
 
I wouldn't be a bit surprised if the flush line sloped backwards a bit.  Just because the flusher spray is going to be located near or at the top of the tank.  Some compressed air would probably clear it if you are worried.
 
Our black tank flusher enters the tank on the right side and washes the grunk to the drain on the other side (great design, BTW  :).)  There's a few feet of piping involved and I'm not sure if water sits in the pipe or not.
 
There should always be a backflow preventer (basically a check valve) in a sewer flush line - the plumbing code requires it. And if the line goes in the side of the tank, the hose is supposed to be routed so that a portion of it is higher than the top of the tank, so that the effluent in the tank can't just run downhill.
 
Thanks for all the replys.  Guess that pretty well answers my questions.  I'd like to shoot a little air through the line but waited too late to start looking for my air blow out plug.  I know I've got one somewhere but that seems to be the $64,000 question, where did I see it last.  By the time I realized I couldn't find it one RV shop was out of them and the other one had already closed for the holidays.  Probably the real question would be just where in the line is the check valve.  Hopefully it would be at the highest point of the flush line so any excess water would either drain into the tank or out where the water hose would connect.  Could Winnebago engineers actually been that smart to do something like that.
 
My tank flush system has a manual valve as part of the input fitting,  (not a check valve) at the flush input (and it is less than effective on mine). There is a vacuum breaker valve at the high point of the line which is, effectively, a check valve and is located about 2 feet above the black tank (and under the bathroom counter in my trailer!!) Since it is high up and admits air into line once the input water pressure is removed,  it allows the remaining water to flow out towards the input fitting . The flush system is otherwise a closed system, not connected in any way to the fresh water system.

 
On mine, the Black Tank Flush line has a check valve right at the hose connection. I supplement tat with another on the hose. Knock on wood, I have not had a problem with the flush line freezing (that I know of) it works everytime.
 
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