Freeze protection for black tank flush valve

[STDevil]

Hi I live in Western Washington where we occasionally get a hard freeze. I was wondering how many if you pump antifreeze through the black tank flush valve, and if it's really necessary. The dealer did not do this when I picked the unit up about a month ago, so I will pump some water through it to see if it has cracked.

I don't know if anyone actually sent water through the valve when the unit was built...

Any thoughts are appreciated!

[Old-Biscuit]

Not necessary
When water is turned off, hose removed then any water on inlet side of Flush Device will drain out
Any water on outlet side of Flush Vavle will drain back into Black tank

Flush Device.....Anti-siphon Vacuum Breaker
When water supply is turned off Air enters allowing drainage

[tpaul]

I force some antifreeze into the line after blowing out with air. In my unit it seems like some of the plumbing to the valve has a low point that could be problematic.

[STDevil]

Originally Posted by tpaul

I force some antifreeze into the line after blowing out with air. In my unit it seems like some of the plumbing to the valve has a low point that could be problematic.

Thank you both! I will pump some antifreeze in just to be safe...if it ends up on the floor of the RV or dripping out, then back to the dealer!

The advice is appreciated.

[NevadaNick]

I have never put af through the black tank flush on any rv i have owned and all but our new one have been through -20 or colder temps.

[bigchick]

i don't. the picture posted above explains why. air can enter at the top and this allows both the input and output legs to drain. you can see the input side draining when you disconnect the hose.

[Rockwood27]

Originally Posted by tpaul

I force some antifreeze into the line after blowing out with air. In my unit it seems like some of the plumbing to the valve has a low point that could be problematic.

I concur with tpaul. Unless you trace both sides of the backflow valve, you won't know if one of the tubes has a low point that won't self-drain.

Sent from my SM-A515U using iRV2 - RV Forum mobile app

[BPTS]

I removed mine, I don't want the massive leak when the $10.00 Chinese piece of crapola backflow device fails or gets debris in it. I have a small double check valve that is on my exterior flush hose*.

*perfectly appropriate & legal- 10 year licensed Backflow Prevention Device Inspector here.