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Reasons Why Your RV Black Tank Fills Up Too Fast

Reasons Why Your RV Black Tank Fills Up Too Fast


The reasons why your RV black tanks fills up too fast have mostly to do with using too much fresh water in the toilet. But there are other reasons too, such as a build-up of solids, too much toilet paper, other sinks draining into the black tank, or you have kids dumping stuff in there that they shouldn’t be dumping.

rv black tank fills up too fast
Dumping the black tank at a campground in Oklahoma

Reasons Why Your RV Black Tank Fills Up Too Fast

A quickly filling RV black tank is a big issue when boondocking because most people want to remain stationary for as long as possible so as to take advantage of the free stay.

Too Much Fresh Water Use

  • When you flush, you are stepping down on the pedal too long. This is probably the biggest reason we know of why a black tank fills too quickly. When flushing down urine, you only need to hold the pedal down for no longer than one second. Two seconds is too much. One option is to turn off the water pump when peeing.
  • You are refilling the toilet bowl with fresh water. There’s no need to do this. True, you may encounter more smell wafting up from the black tank, but then again that’s why RVs have roof vents and why they sell candles at Walmart. You can also put in more black tank enzyme. Enzyme packaging usually gives conservative directions for use. Put in more if the smell is that bad.
  • You’re wasting water trying to rinse off skid marks. Instead, use a spray cleaner and wipe it off with RV toilet paper. Or if you don’t mind, leave it there for your husband to “piss off”.

Using Too Much Toilet Paper

  • You’re certainly free to use as much toilet paper as you want, but if you don’t want to have to dump your black tank too often, then learn how to use less TP.
  • Or better yet, don’t dump it down the toilet. Keep a separate waste bin for paper products, then burn it in the campfire.
  • You’re using the wrong toilet paper. Standard household toilet paper can take weeks to fully render into pulp. Meanwhile, RV-grade toilet paper is designed to breakdown into pulp in just hours.
  • Adding more black tank enzyme will help expedite the breakdown of toilet paper.

You Have a Build-up of Solids

  • If it seems like your black tank is filling up faster and faster over the months (or years), then you could have a build-up of solids.
  • This is a common occurrence with RVs that spend a lot of time in RV parks and developed campgrounds. This is because RVers tend to leave the valves open on their black and gray tanks. As a result, the “poop” in the black tank doesn’t have enough liquids to break it down and flush it out. Do a Google Search for “RV poop pyramid” to understand this better.
  • It can also happen with full time boondockers, particularly if their RV has a small black tank. Small tanks fill up faster, and as a result, does not give enough time for solids to completely break down.
  • Use an “RV Swivel Stick” (see it on Amazon) to break up the solids and flush them out. Use this each time after you have dumped the black tank to keep it free of build-ups.
  • Make sure to use plenty of black tank enzyme to prevent solids from building up more.

Your RV Has Other Sinks Draining Into the Black Tank

  • Some RV manufacturers will plumb one or more sinks into a black tank. This was done for logistical reasons based on where kitchens and bathrooms are located in reference to a black tank. Usually it’s because a sink drain did not have enough descending slope to reach a gray tank, and thus was plumbed to the black.
  • To determine if you have another sink draining in your black tank, start by draining your gray tank. Once empty, leave the gray tank drain open. Now, turn on one of the faucets in the RV. If you don’t see any water flowing out of the gray tank, then you know it’s draining into the black.

Your Black Tank Gauge is a Liar

  • Gauges designed to tell you the level of contents in a black tank are terribly inaccurate. The RV industry uses very cheap sensors that deliver poor results.
  • Even though your gauge is saying your tank is completely full, it may only be half-full.
  • The only way to tell for certain how full a black tank is, is when it backs up into your toilet. When the contents of your toilet won’t drain, it’s almost always because the tank has reached its full capacity.
  • At this point, try to remember the last time you dumped the black tank and figure out how many days had gone by. Now you will know how long you can make a black tank last.
  • If you’re out boondocking and you find that sewage has backed up into your toilet, the only solution is to release just a little bit of your black tank, enough to let the toilet bowl drain. Or, scoop out the sewage from your toilet bowl and dump it outside. The “environmentally correct” solution is to use a “portable RV waste tote” (see it on Amazon). This is a usually a 30-40 gallon tank with wheels on it that you can pull (by hand) to a dump station. But for boondocking, you will only need a small tote, no more than 12 gallons (see it on Amazon) to hold the 1 or 2 gallons needed to let your toilet flush, then store it in the back of your pickup until you can get to a dump station.

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