If You Want More Fresh Water

[I-RV]

If your fresh water tank is connected like mine, the bottom 25 gallons cannot be used because the pump starts sucking air (see photos). This means we are carrying around 208 useless weight.

To get more water into the tank, you can fill it to the "F" light comes on, but this is only 83 gallons and with the bottom 25 gallons being useless, you have 58 gallons to use.

Next you can crawl down on the ground to take those blasted pins out of the latches to watch the tank fill. Now you have 75 useable gallons.

Rather then deal with those latches, I once just filled the tank until I saw water coming out of the overflow, beneath the RV. I shut the water off and was amazed that water kept coming out for several minutes. I quickly found out that the overflow siphoned the top 21 gallons out, leaving me with 79 gallons and 54 useable.

Well where is this going??? I cut 7 1/2 inches of the overflow tube off (from the floor up) that protrudes through the floor. Enlarged the hole (with rat tail file) for a 3/4" PVC pipe. stuck the cut overflow tube into it and hung it with a tie-wrap. Tried to use few tools.

Now the tank can blindly be filled until water comes out the tube. Then when the water is shut off, there will be no siphoning action. You will have 100 gallons with 75 useable.

I know that many do not want to carry 100 gallons, but for those that do, here is a filling method.

[AREA51]

I-RV.
You are a genius!
GOOD LUCK
AREA51

[spitbarnatt]

Interesting, not had mine long but have normally used the fill up till overflowing method. Didn't realise I was losing that much water. Will have to open that side up and have a look now. Thanks.

[dan-nickie]

Thanks. Great info.

[tnbendr]

Now I know why mine kept draining after filling to much, couldn't figure out why it didn't just drain down a little.
You are a smart cookie to figure that out I-RV! Well definitely do that mod soon.

[speedmerchant]

Brilliant, thanks!

[nathantoensing]

Fantastic! Thanks for sharing!


--Nathan
2016 38a

[accumack]

I'll be doing mine soon. Thanks!

[Campin Cajun]

Nice mod.

For those who will not try this, you can see your FW tank level from the DS wet bay. It's right behind the sewer and gray dump valves.

[lefaivre]

Well done ... let me guess, an engineer?

[I-RV]

Originally Posted by Campin Cajun

Nice mod.

For those who will not try this, you can see your FW tank level from the DS wet bay. It's right behind the sewer and gray dump valves.

If you fill the tank by whatever means to 100% by eyeballing it, you will loose 21 gallons without knowing it, upon driving. As soon as you made a left turn, the small volume of the overflow would quickly fill due to the movement of water, and siphoning would begin.

The anti-siphoning scheme in post #1 will prevent that.

LOL - I thought that you had me there, Campin Cajun

[purduepete97]

Don't own one of these things, but wondering if you can regain use of the last 25 gallons be repositioning the fitting that the pump connects to (i.e. to come out the bottom of the tank instead of 20% of the way up the sidewall)???

There are probably obstacles in the way preventing you from doing this, but then again sometimes the obvious fixes are the easiest to overlook. Doing this relocation + the antisiphon fix would give you use of nearly all 100 gal (in theory!).

[15berkxl]

Originally Posted by I-RV

If your fresh water tank is connected like mine, the bottom 25 gallons cannot be used because the pump starts sucking air (see photos). This means we are carrying around 208 useless weight.

To get more water into the tank, you can fill it to the "F" light comes on, but this is only 83 gallons and with the bottom 25 gallons being useless, you have 58 gallons to use.

Next you can crawl down on the ground to take those blasted pins out of the latches to watch the tank fill. Now you have 75 useable gallons.

Rather then deal with those latches, I once just filled the tank until I saw water coming out of the overflow, beneath the RV. I shut the water off and was amazed that water kept coming out for several minutes. I quickly found out that the overflow siphoned the top 21 gallons out, leaving me with 79 gallons and 54 useable.

Well where is this going??? I cut 7 1/2 inches of the overflow tube off (from the floor up) that protrudes through the floor. Enlarged the hole (with rat tail file) for a 3/4" PVC pipe. stuck the cut overflow tube into it and hung it with a tie-wrap. Tried to use few tools.

Now the tank can blindly be filled until water comes out the tube. Then when the water is shut off, there will be no siphoning action. You will have 100 gallons with 75 useable.

I know that many do not want to carry 100 gallons, but for those that do, here is a filling method.

How long is the 3/4 inch pipe and how far are you inserting the overflow into the pipe?

Wayne

[accumack]

I just went out to look at mine I have an 84 gal tank but I didn't see where the over flow comes out. I have to investigate further when it's not 100º out.

[Campin Cajun]

Originally Posted by I-RV

If you fill the tank by whatever means to 100% by eyeballing it, you will loose 21 gallons without knowing it, upon driving. As soon as you made a left turn, the small volume of the overflow would quickly fill due to the movement of water, and siphoning would begin.

The anti-siphoning scheme in post #1 will prevent that.

LOL - I thought that you had me there, Campin Cajun

I once filled my FW tank so much that the tank had a dome on top. It rose like an apple pie. Strange thing was that not a drop came out the overflow line. I thought my overflow was plugged up, so I drained the tank some and stuck an air hose in the overflow line and it was not plugged up. Go figure that one out??

[accumack]

I found it bulges unless I have a faucet open partway.

[CAT-RN]

I cut a hole in the back wall of the basement bay in front of the water tank on the passenger side. Open the bay door & look thru the hole and you can see water tank fill up.

Just raise your driver side of the coach with the jack an inch. Probably get all the water then.

As to the overflow tube. I just slid it up above the tank & wire tied it there. Drilled a couple 3/8 holes on floor along with the hole where it was. If I overfill tank and it runs over. It just runs out the holes. Don't syphon anymore.

Russell

[15berkxl]

Originally Posted by CAT-RN

I cut a hole in the back wall of the basement bay in front of the water tank on the passenger side. Open the bay door & look thru the hole and you can see water tank fill up.

Just raise your driver side of the coach with the jack an inch. Probably get all the water then.

As to the overflow tube. I just slid it up above the tank & wire tied it there. Drilled a couple 3/8 holes on floor along with the hole where it was. If I overfill tank and it runs over. It just runs out the holes. Don't syphon anymore.

Russell

Russell what if you did that but added to the length of the overflow tube would it still siphon


Wayne

[I-RV]

Originally Posted by 15berkxl

How long is the 3/4 inch pipe and how far are you inserting the overflow into the pipe?

Wayne

The water tank is 6" high, so I cut the overflow tube 1 1/2" higher then the tank (thus no siphoning). This cut was about 1" below a tubing hose clamp, screwed to the frame. The clamp position may be different on every MH, since they probably eyeball install it. I use about 11" of PVC. The only matter is that the overflow is inserted in it and that the PVC protrudes an inch or so below the cargo floor. I drilled a small hole in the top of the PVC to insert a tie-wrap, which wrapped around the present clamp.
Hank

[I-RV]

Originally Posted by 15berkxl

Russell what if you did that but added to the length of the overflow tube would it still siphon
Wayne

I wish that Russell would elaborate more on his tubing location. As for how siphoning works, three things need happen. First the output must be lower then the input. Secondly, liquid must be higher then the tube's input and lastly, the tube must be primed by being filled with liquid.

Siphoning will happen with these conditions and will continue until either the output tube is raised higher then the liquid level or liquid in the tank falls below the tube input.

Since we do not want siphoning is why the tube is cut 1 1/5" higher then the tank.