2022 301UBH black tank flush line broke?

[Dirtflinger66]

Was wondering what the pipes can take for pressure cause I went to flush black tank on rear 1/2 bath and the line under the sink leading to the tank blew the 90* fitting and got water everywhere? Granted they bent the pex line to fit it to the 90 putting extra strain on the fitting but should I regulate the line pressure to flush or should it be able to handle city pressure? Any info and help is appreciated. I’m going to redo it in brass fittings and pen clamps, but I don’t want to bust any others.

[chuckster57]

1/2” pex is rated at minimum of about 480 PSI. I wouldn’t want to be the one testing. I believe it’s the fittings that fail. I would use a pressure regulator and in this case a cheap one would be ok since it’s only going to be used to flush the black tank along with the hose.

[travelin texans]

Most likely the issue was the anti siphon valve on that line was either faulty or backwards.
I'd recommend removing it & replacing with 2 Shark Bite 90s & use the water hose type back pressure fitting at the hose connection with a pressure regulator.
As Chuck stated you'll never exceed the pex piping pressure, the cheapo plastic fittings will give way long before the pipe.

[JRTJH]

If your RV is still in the OEM configuration, there "should be" an anti-siphon valve in the 90 degree fitting location. It is, without a doubt, the weakest link if the entire water supply system. If it looks like this photo, it's that "egg fragile" device. If not, then possibly somone has already replaced it with a conventional fitting ?????

As for future use, I think most people would agree that the PEX lines are sturdy enough to withstand most "city water pressure"... It's those "danged" plastic connections and fittings that are your "weakest link". Squeeze a bit too tight on a clamp, put a little too much pressure trying to align pipe ends, vibrate the fitting while towing and just the flexing and torque can set up an almost guaranteed failure....

THEN, to add insult to injury, the terminal spray head and fitting in the black tank is also plastic, so even if you do replace "everything in the flush system with brass fittings to eliminate problems with pressure damage.... Get that pressure to the plastic spray head, snap it or crack it and all the work to enhance the survivability is for naught.... Any chain is only as strong as its weakest link....

The term "city water pressure" is, at best, an estimate that can mean most anything. In some campgrounds, during the day, "city water pressure" is around 50-70 PSI, but at night, when the neighboring community is not using water and the campground is "sleeping", that pressure can creep up to well over 100 PSI. In Marquette Michigan, there's a city owned campground with a large industrial complex behind it. When that complex shuts down at 5PM, city water pressure in the campground rises significantly. We saw our regulator input pressure rise to 140 PSI during one stay in that campgorund.
So, don't rely on "city water pressure" and especially don't trust an RV water system to "be OK" on an unknown "city water system"...

Most people use a pressure regulator adjusted to 40-50 PSI for all water supplied to the trailer. Anything greater has the potential to cause problems wtih leaks.

Here's the photos of the anti-siphon valve and the black tank spray nozzle and the type of water pressure regulator you want to consider.

[Dirtflinger66]

Ok I’ll check the anti siphon but I believe it in correct. I’ll regulate it down and check it after repairs are done. Thanks everyone for the responses.