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Old 01-13-2020, 09:57 AM   #1
TahoeBound
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M.O.C. #21656
2018 Montana 3790 Black Tank Dump Valve

Hi everyone, has anybody replaced the black tank dump valve on their 2018 3790 yet? My cable has been very tight for about a year and I've tried everything to free it up. Trying to figure out what size cable/valve to order. We are full-timers and are need to fix this issue before we head out in the spring.

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Old 01-13-2020, 10:22 AM   #2
jcurtis934
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Not a 3790 owner, but the plumbing is generic to all models. Black and shower grey are 3 inch valves. Most cable runs are 6 feet. Dropping your bottom will reveal all to you.
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Old 01-13-2020, 10:48 AM   #3
Carl n Susan
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A Search on "black tank valve" or such will uncover a number of discussions about this fun exercise. You might just need a new cable as it is the part that is the stuck.hard to pull source. If the tank is leaking then a valve replacement is in order.


You will want to drop the coroplast at the rear of the dropped section to uncover the valves. You only need to undo about 3' of it to get access. If you have the "nails" rather than Tec Screws holding the coroplast to the frame, then do another Search to find the trick on removing them (and replace with Tec Screws).


Be sure to raise the front of the RV, drain and flush the tank, and then drop the nose below level before you start. That will help keep things that should be in the tank, in the tank.



What cables?

http://www.montanaowners.com/forums/...ack+tank+valve



Other tips:

http://www.montanaowners.com/forums/...ack+tank+valve (Post #3)
http://www.montanaowners.com/forums/...valterra+valve
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Old 01-13-2020, 11:09 AM   #4
Old Dad
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I had purchased and prepared to replace my black tank dump valve a few years ago due to the same problems it sounds like you are having. After dropping the coroplast, I found the rubber in the valve was not aligned properly. I disassembled the valve, greased the rubber and reassembled. It has worked properly since that time.
My valve was leaking as well. I found some trash from original construction packed in the valve seat. This wasn't a "fun" job, but I believe it is easier to clean and grease than replace.
Good luck.
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