Trailer shook with a boom

[Mr Mustang]

Originally Posted by Pitchbb9

2010 3400RL
I had just drained my black tank and was backwashing the tank. I heard a boom / thud and the RV moved a little. I thought the worse, my tank had fallen and the connections have cracked. I immediately went out and pulled the drain and shut the flusher off. I observed water dripping from the underbelly.
I have pulled down the underbelly sheeting and found my tank has not fallen and appears to be intact. The connection for the stool looks good. I have not looked at the vent connection yet.

Any Ideas?

Could there have been trapped air in the tank and it was forced out of the vent connection?

Maybe there is a hairline crack that I haven’t found yet?

Let us know what you find please

[Mark7]

I have had all 3 tanks out of my ‘04 3295RK. Not a real big job if you’re handy, but not a lot of fun.

Buy a “flush cut” saw to make the job a lot easier.

Here is a link to a post I made in another thread to illustrate tank construction, failure, and if you look closely how they are healed in place.

https://www.montanaowners.com/forums...7&postcount=24

[hosssmith]

Originally Posted by Carl n Susan

The tank will come out from under the rig. There is no need to remove the floor above it. As others have written, the top of the tank has separated from the tub and likely will need to be replaced.

FYI, I've only done this ---- twice .

I have only one word for you. TIMER. I start the flush water for 1 minuet then pull the drain open and let it run till barely anything can be seen running out. Close the drain valve for 4 minuets then drain again and continue that pattern until the effluent runs clear.

After blowing up two (nobody ever accused me of being a fast learner) black tanks I use the timer on my phone and nothing distracts me anymore when dumping that tank.

[twindman]

4 to 5 minutes is what I also use. I too blew up one when I got distracted and let it run too long. Another broke apart when I traveled on some rough roads with 1 day's 'stuff' in it. Smelly!

[Montana Man]

Its really unfortunate that Keystone installed tanks for so many years that fail so easily. My buddy had a tank replaced for the second time. We filled it right there at the dealer and it failed again on the spot. They blamed us saying waste tanks can only be filled half to three quarters full. Long story short, they paid a local rv repair shop to rebuild the mounting brackets and install new tanks.

The two piece tanks are not installed properly even if they don't break apart. Additional support is needed to eliminate this kind of failure. A search of this forum will reveal several fixes for this issue.

[WeBeFulltime]

If you have to replace the tank try to do it with one of the one-piece tanks like are used on the newer Montana fivers. Our 2018.5 3791RD had the new type.

[Leaseit]

A note about the 2009-2011 3400RL. Under the black and gray tanks are two channel iron bars from left frame to the right frame where they are bolted on. They are there to support the bottom of the tanks even though the tanks have mounting flanges on the top.
I have never run with anything in those tanks, but one day noticed the channel irons looked like they were bent down some. I checked a new 3400 at a dealer and the channel irons were totally straight. Spoke with service guy. He told that, yes they bend down after time and that the unsupported weigh cause tanks to crank.
His recommendation was replace them with "proper" channel iron bars to support the bottoms of the tanks. 1 x 4 3/16 inch structural channel.
You might want check these bars while your doing any work under the rig and make sure the tanks are also supported from underneath.

[mhs4771]

I was using the timer method when flushing the Black, then realized that wasn't good, because of not knowing the flow rate, which some places being rather low and other with a fire hose flow rate. So I purchased a little inline flow meter from Amazon, now I know exactly how much water I'm putting in when flushing. BUT no matter what you use, DON'T walk away!!!!!!

[jbailey24]

After mush discussion with "elders", I purchased a sleeve that fits in the toilet bowl and allows the black tank to fill after the original flush and rinse. By filling from the top, I don't have to worry about over pressure, and can fill the black tank completely. Two runs of 30+ gallons completes the flush, and allows me to put about 5 gallons for "sloosh cleaning" going down the road.

[drog55chev]

I guess I've lucked out. I usually flush my black water tank with the drain open but I close it for 30-60 seconds and repeat this process several times. However one time I got distracted and left it closed for a lot longer than I should have. I turned off the water and opened the the drain. OMG, the flex hose sprang to life, came out of the ground connection and sprayed all over the place. Reminded me of a fire hose that nobody is holding onto whipping around. I thought most of the pressure would go up through the vent pipe but it surely didn't. Glad I didn't try and flush the toilet at that time because I'm sure there was pressure behind it too. I still do this cycle but am cautious on how long and even short cycles now I make sure I have the ground connection secured because it still seems to release pressure. Knowing now how these tanks are made I may not do that anymore.