Bad smell by dump valve

[rberg]

We have a Jayco trailer with the four season package (it's insulated underneath) and now we have a bad small, somewhat sewer-like, near the dump valve (sewer hook-up). We have flushed the trailer black holding tank several times and dump it after every camping trip before we leave the RV park and still we have this bad smell. I have power washed the underside with Pinesol and water and it still smells.
What do I do now?

[rberg]

My concern now that you have given me a couple of possibilities, is that the "stuff' has dried and may never come out of the insulation. The dealer can't find it after about $150 worth of labor and parts. I am tempted to just rip off the insulation and leave it off, since we don't camp in the winter anyway.

[cbshoestring]

Another possibility is a hole in the drain pipes, allowing some stinky stuff to get trapped between the trailer floor and the under-cover. You could poke a small hole in the cover, near the dump valve, see if you get leakage....when dumping. Just remember to patch the hole...or refer to the above.

[Mr__Camper]

Check the underbody for a hole that may have allowed something to crawl up and die.