How to Unclog a REALLY Clogged RV Sink Drain?

full sink of water

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Recently our RV’s bathroom sink stopped draining.  OK it drained a little bit but it was VERY slow. Definitely a clogged drain!

No problem, we thought, we’ve had clogged drains in our RV before.  We got this.  So, we did what we have done in the past.

Before we start, let’s talk about what not to do – you definitely do NOT want to use something like Drano in your RV – it is far too caustic for the RV plumbing system. 

What We Tried First (Or What We Used to Do)

  • Pour about ¼ cup of baking soda down the drain immediately followed by about a cup of vinegar.  It will fizz like crazy but doesn’t create any poisonous gases.  Let it sit for about 10 minutes and rinse.  
  • Pour hot water down the drain.  
  • Remove the P-trap and clean it.  This is easy to do but kind of gross and stinky.  I wear gloves.  
    • Put a small bucket or dish washing bin under the trap (the U shaped pipe under the sink) to catch the water that is in it.   Unscrew the sides of the trap by hand and put it in the bucket.  Take the bucket outside and clean out the trap. 
    • An old or cheap toothbrush is great for loosening the goo.  We keep these six packs of cheap toothbrushes on hand for miscellaneous household projects like this.  Actually I use them to clean the upper part of the sink drain that is hard to get into too.  They’re super cheap! 
    • Rinse with a hose and replace the trap.  

Uh oh!  The drain was still clogged and very SLOW to drain.

We have never had such a stubborn drain clog – in the past any slow drainage issues were easily resolved by following the steps above. 

What finally Unclogged the Drain?

This awesome sink & shower plunger!  I’ll admit I was skeptical but it worked incredibly well. 

Master Plunger MPS4 Sink Plunger

We opened the grey tank valve (while connected to a sewer connection), filled the sink with some water and started plunging.  

The plunger has the space for 4 cups of water so you can really push and pull a lot of water through the pipes to clear any clogs.  It felt like it was actually the pulling action that cleared most of the clog (and pulled gunk into the sink).  

Sure enough, the plunger pulled a lot of gunk out of the drain and within 5 minutes the sink was draining again!  

Next time I’ll be jumping right to the plunger!  

It was a five minute fix and easy!  

Other Possible Causes of a Clogged Drain in an RV

Check the inline vents and the roof vents. – Poor venting can cause slow drainage and stinky sewer smells.  

Inline vents can wear out and ours were fairly old so we replaced both the kitchen and bathroom inline vents.  

The inline vents are located under the sink above P-trap – they screw off and back on again pretty easily.  You’ll want to add a bit of vaseline or plumbers tape to the threads to make sure you get a good seal.

If we hadn’t wanted to replace them anyhow we would have taken the inline vent off of the kitchen sink temporarily and put it on the bathroom sink to determine if it resolved the issue.

Roof vents can get clogged with debris or something like a wasps nest. So use caution when checking for a blockage.

That’s it for now. The sink and shower plunger is definitely a keeper and will be the first thing I grab if our drains are ever clogged again. I might even plunge the drains once in a while just to make sure they stay clear.

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