Saturday, December 2, 2023


Stop guessing! This water meter won’t let you overfill your tanks

By Kate Doherty
On our first trip out three years ago, when it came time for us to refill our fresh water tank, we waited until the fresh water overflow spilled over, letting us know the tank was full. That meant we guessed and babysat the process. And after voiding our black tank and flushing, we needed to add a few gallons of fresh water into the black tank.

One neighbor who came over to chat said count to 100. Another said he uses his watch and times one to two minutes. Both individuals meant well, but when water volume and pressure differ from park to park, campground to campground, trusting their methodology was unreliable.

Finding a better methodology

It didn’t take us long to look for a more precise method of filling the tanks. We’ve witnessed folks’ fresh water tank spilling water back out. After perusing online forums, it became apparent that plenty of folks are not aware that a simple water meter can make life easy and avoid possible backflow.

We bought the Save A Drop P3 Water Meter and have used it ever since. Now we refill our black water tank each time with exactly 3.8 gallons. You could do the same.


Maintain a safe water supply onboard your RV





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Brian (@guest_158953)
1 year ago

I have one and found it to be consistently 10% low in measuring at any pressure. Not a big deal as I just do the math, .9 equals 1 gallon. Once I figured out the seconds per gallon I now just time it at 40 PSI, 1 gallon every 12 seconds or 5 gallons per minute, close enough for me.

Roger Marble (@guest_147065)
2 years ago

I’m happy with my Save a drop unit. When using the black tank internal sprayer to do a final flush before winterizing the RV, I use this to get the tank about 3/4 full, add some Dawn and borax and let that mix sit for a few days. I don’t let full pressure go through it. I do connect to the tank spray connection that has 2 backflow limiters in the line and I installed the external connector on the outside of the RV after I sprayed it red and placed the warning sticker next to the hose hook-up.

Larry (@guest_146296)
2 years ago

Bought one of these. Couldn’t get it to stop dripping at the faucet. Changed the washers and still didn’t help. If you leave on all the time you will be wasting a lot of water. I don’t recommend.

Rusty (@guest_128141)
2 years ago

What I did is time the flow of water at 40psi to fill a one gallon bucket. Now days, I just fill to the “oh that is full enough” level. Dump a few squirts of Dawn Dish soap in black tank with gallon or so of water let the sloshing begin as the road appears.

Tom Horn (@guest_127431)
2 years ago

Don’t count on the accuracy when filling. The meter will show 4.2 gallons when 5 gallons have been run through the meter and hose.
Don’t count on this device when flushing your black or grey if you like to fill them up before pulling the handle.

Last edited 2 years ago by Tom Horn
John Koenig (@guest_127342)
2 years ago

I bought one of these and, the first 5 or 6 times I used it, I was very happy with its’ performance. The next time I used it, it “popped” apart and, I could NOT get it to stay together again. Reviews on Amazon showed LOTS of buyers had the same experience. Until a better quality unit is made, I won’t be wasting any more money on one.

S danford (@guest_127141)
2 years ago

I went thru 3 of these in 2018. They crack. Don’t know if they’ve improved their manufacturing or not.
it did work accurately before the crack

Scooter (@guest_127130)
2 years ago

Easy enough to use the belching water technique. I top off at home so any overflow waters my tree. I can see a nice use of determining how much water used. I track my power usage why not water too?

Drew (@guest_127122)
2 years ago

I prefer to add 3.7 gallons.

RV Staff
2 years ago
Reply to  Drew

Well, then you definitely need one of these water meters, Drew. 😆 Have a great day! 😀 —Diane

James Starling (@guest_127138)
2 years ago
Reply to  Drew

Fill toilet with a 1 gallon container. Now each time you flush you will add 1 gallon till you reach recommended amount in black tank, between 2 and 3.8 OR 3.7 gallons.

Drew (@guest_127293)
2 years ago
Reply to  James Starling

Appreciate it James

Alpenliter (@guest_127120)
2 years ago

Ok, to all the naysayers on here, I feel I must speak up. On many RVs, the vent on the fresh water fill does mot keep up with incoming flow, causing the water to pour out of the filler and/or “belch” out the excess, before actually being filled. This device allows you to know how much water actually is in the tank. I have a 100 gallon FW tank that starts the belching at around 35 gallons. Adjusting the flow and monitoring with this device allows me to know I have a full tank.

friz (@guest_179326)
1 year ago
Reply to  Alpenliter

Is it really a problem/issue if at most a quart of water overflows from the fresh water tank when filling? Nice gadget I suppose but not a real need for it.

Dave Helgeson (@guest_127113)
2 years ago

One of the best uses for a digital water meter is determining your water usage to help you become a better dry camper. Here’s a blog I wrote about it.

Bill (@guest_127228)
2 years ago
Reply to  Dave Helgeson

we’ve used one of these since 2015 and it comes in really handy a lot! I use it every time I refill fresh water so that I know exactly how many gallons and how much weight I am adding (we “boondock about 90% of the time, just hitting parks for laundry and sometimes lux showers).

Wolfe (@guest_127094)
2 years ago

I just don’t drain black to the very last trickle. Faster cheaper easier.

Now, if you put a water sensor on the overflow or tank monitor, which then turned off the shore water with a solenoid, that might actually do something….lol. Complex nerdy overengineered. 🙂

Nanci (@guest_127093)
2 years ago

This would be great for the added “flushing” of the black tank. I know I am NOT supposed to ever close the slide valve when flushing, there is even a label on the motorhome door telling me not to but, there is still a lot of gunk stuck to the sides of the tank. I close the valve count to 200 hundred and pull. With a water meter I would feel more comfortable adding more than the “200” count.

Don (@guest_127089)
2 years ago

Hard to imagine a less significant problem, nor spending money to “solve” it. Sorry, but this is a total bust…

Don (@guest_127090)
2 years ago
Reply to  Don

PS: I sure hope you’re not using the same meter to fill potable and to add water to the black tank! THAT is a serious issue…

Crowman (@guest_127086)
2 years ago

Looks like a solution looking for a real problem. That isn’t a real problem.

Tommy Molnar (@guest_127108)
2 years ago
Reply to  Crowman

Exactly right Crowman . . .

Dan (@guest_127078)
2 years ago

Hmmm? I can’t grasp the need for this. In order to use it I have to know the capacity of my fresh water tank and how much is in there when I go to fill it. And then, what’s the difference between watching for the overflow and watching this little meter? Maybe I’m missing something here.

Ceil (@guest_127371)
2 years ago
Reply to  Dan

Maybe this will convince you. I read two recent horror stories on iRV2 where the owners thought they could just stuff a hose into their fresh water inlet and walk away. Then when water poured out of the vent, they knew it was full. Well both of their tanks exploded and came off the rails. The water pressure going in was too fast and not enough air was exiting out. The tanks ballooned up. We always use a water gauge on a silicone extension so air gets through and we don’t blast the water.

Dr4Film (@guest_127074)
2 years ago

I don’t need to purchase another device in order to prefill the black tank after dumping. Waste of money! Simply flush the toilet and let the water run for a spell then close the toilet. Add what ever chemical of your choosing then flush one more time. This is not rocket science people. I like using the RV Rid-X for our tanks. I really like using Happy Camper’s but they stopped making the product.

Tom Moelly (@guest_127075)
2 years ago
Reply to  Dr4Film

I agree this is just another gadget .Why is it complicated to add water to your tanks.

Tony Grigg (@guest_127096)
2 years ago
Reply to  Dr4Film

FYI – Happy Camper is still quite available from Amazon, Walmart, etc.

Ceil (@guest_127373)
2 years ago
Reply to  Dr4Film

Happy Camper is still around. Order from Amazon.

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