Black tank flush not working

[Raptor06Dave]

2006 raptor 3712. I can’t locate the “check valve” or back flow preventer can any one help used the flush earlier this season and worked fine. Last week when I hooked it up nothing but a small leak at hose connection. Line from hookup goes up into wall in by toilet. Help and thanks

[dadnjesse]

Look up under the sink sometimes there hard to see. Should look like this.
https://www.recpro.com/rv-vacuum-bre...571-vac-chk-a/

[Raptor06Dave]

First look didn’t find it will do a more thorough look will remove access panel be kitchen sink

[JRTJH]

Originally Posted by Raptor06Dave

First look didn’t find it will do a more thorough look will remove access panel be kitchen sink

Typically the backflow valve is under the vanity. If it is, you'll see 4 PEX tubes under the vanity, it's there, usually "way up top, behind the sink bowl". If you only see two PEX tubes, then it's either located in the wall, behind the shower faucet. If it's in the wall, it's usually a "common shared wall" and one side will have a cabinet mounted over the backflow valve with an access panel on the back wall of the cabinet.

I'd first "count the PEX tubes in the vanity"....