Visiting family but need to empty your RV black tank? It is possible to use a house's sewer clean-out for dumping. Here is how.

Remember that scene in the Christmas Vacation movie where Cousin Eddie emptied the black tanks of his Class A wreck of an RV into the city sewer outside Clark Griswald's house?

Well, it's possible. Sort of. But not at the curb down a sewer grate where cousin Eddie did the RV dumping but in what's known as a sewer clean-out that most houses have.

Fulltime RVer Campskunk wrote about doing just that a few years ago. Here's an update to that post.

How to empty your RV black tank in a house sewer clean out

Houses have connections that come in handy for us RVers staying at a residence, and I'm not talking about the electricity and water. I'm talking about sewer connections you can dump your waste water tanks into.

City sewer connections have what's called a clean-out, which is a large opening into the sewer line just as it leaves the house and heads toward the city sewer connection.

It's perfect for dumping your gray and black water tank contents if you don't want to drive across town and give people money, which is usually what you have to do when dumping in a populated area.

The trick, however, is to find this clean-out, because few homeowners know where they are.

Finding the house sewer clean out

In houses with connections to a municipal sewage treatment system, the sewer line comes out from under the house and usually makes a bee-line for the street where the sewer lines are.

If you're in the middle of the block this is easy – corner lots could go either way.  Water meters are another utility usually on the side of the lot where the sewer hookup is, so that will help give you a clue to location.

Get a little shovel and gently poke around in the flowerbeds and other stuff along the base of the house's foundation.

The line is usually just below ground level, and is a 4 inch PVC pipe (probably cast iron up north where the ground freezes – one of you Yankees help me out here).

It's the only huge pipe coming out from underneath the house – supply lines are much smaller.

There will be a four inch white plastic screw-in cap with a square protrusion in the middle. 

Once you have found it, clear enough dirt so none goes down into the pipe when you open it, and get a big wrench or pliers and unscrew the cap. 

Pull your RV up so that your emptying hose will reach the clean-out, and dump away to your heart's content.  

Replace the cap and the dirt, remove any evidence of trampled flowers before the homeowner sees them, and you're done.

By the way, for you vans of the movie… here is a YouTube clip of that iconic Cousin Eddie scene:

It could be illegal to do RV dumping like this – Check local laws

I have heard of, but never encountered, municipalities where this is illegal – check local ordinances before you do this.

There's also a huge difference between city sewers and septic systems.

For one thing, with a septic system, the clean-out is going out the back of the house to the septic tank and drainfield, not out the front to the street.

Using a House sewer connection for RV dumping has limitations

Secondly, septic systems can't handle giant loads of water, so 30 gallons from a smaller Class B or Class C RV should be no problem, but make sure they aren't all taking showers and washing clothes inside when you do it.

Thirdly, make sure you use the clean-out upstream from the septic tank, as close to the house as possible. If you dump into the septic tank itself, do it upstream of the baffle. Dump into the drainfield and you'll probably be invited to stick around for the dig-up-the-drainfield party – as the guest of honor. You don't want this distinction.

When in doubt, drive across town and use the RV dump.

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