Fresh water overflow?

If you are losing water out the vents while traveling, it is not a siphon, it is simply a spill that occurs while rounding a curve or driving up or down hills. Many thousands of RVs have been built with the vent pipes attached at the top of the tank and then go straight down and out the bottom. Of course when the "bucket" is tilted, water spills out. The proper fix is to run the vents out the side well above tank water level. Putting valves on vent pipes is a dangerous idea, one time doing it wrong will cause severe damage. Notice that I said "pipes" as in two or more, if there is only one then that too is wrong because the venting should have twice the capacity as the supply line.

The pickup point for water supplied to the pump should be on the bottom, many are on the side which doesn't allow full use of the tank capacity. The fix is to plug that port and attach the hose to the drain port with a tee.

laknox wrote:


I also prefer a gravity fill but I've also found that it's much better to fill your tank =slowly=. I'm pretty sure that the first time I boondocked with my new KZ, which doesn't have a gravity fill, I managed to siphon out a goodly portion of my fresh water. I was filling and got a good flow out of the overflow but, even being as water-conscious as possible, we managed to run out of fresh water in just 4 days. I'm =supposed= to have 61 gallons, total, and I plan on getting a meter to check that I'm actually getting 61 gallons. Next time I have it at the house, I'm going to check, then drive around a bit with someone following me to see if I get any siphoning. Then, I'll measure what I get from the low-point drain. I've read more than once on here that people expect to have a tank of X gallons but end up with one that's X-10 or 15 gallons.

Lyle

Check where your pump draws water from the tank. On mine, the fitting is on the side of the tank so the pump will start sucking air when there is still about 1" to 1 1/2" of water still in the tank. That works out to about 7 or 8 gallons of water. If I need that last bit of water, I just adjust the levelers to put the driver's rear corner low enough for the pump to draw more water. Just not more that 3 degrees off level as that would cause issues with the fridge.

You can put water in the tank faster than the overflow can let it out. I once saw someone walk away from their trailer while filling the water tank. The tank over-filled and bowed the floor inside the trailer because the overflow couldn't handle the input. I suppose the tank would have eventually ruptured if left any longer. Luckily, there didn't appear to be any damage to the floor.

On the subject of vents/drains, can someone explain why my unit doesn't have low point drains like older units that I'm familiar with?

laknox wrote:

Given the "standard" quality of most mfrs, it wouldn't surprise me at all if a bit of the overflow pipe/hose got stuck down into the tank a bit, which =would= siphon, once it got started. As a former farmer who used siphons from 1" to 4" in size, it's amazing how little head difference it can take to run a siphon.

Lyle

In that case, I'd fix the overflow instead of putting in a ball valve. Have you ever noticed what a bag of chips does as you head into the mountains? just sayin...

camperdave wrote:
The vent is at the top of the tank, I don't see how it can siphon out. Maybe splash a bit out, but even then just re-route the vent to loop up a bit higher if it's a problem.

I'd be super leery of valving off the vent, even if only for travel.

Given the "standard" quality of most mfrs, it wouldn't surprise me at all if a bit of the overflow pipe/hose got stuck down into the tank a bit, which =would= siphon, once it got started. As a former farmer who used siphons from 1" to 4" in size, it's amazing how little head difference it can take to run a siphon.

Lyle

The vent is at the top of the tank, I don't see how it can siphon out. Maybe splash a bit out, but even then just re-route the vent to loop up a bit higher if it's a problem.

I'd be super leery of valving off the vent, even if only for travel.

TazFord wrote:
Thank you everyone. I was just leary of overfill after hearing stories of damaging RV’s. Now I know and I found them dangling by my drain plug as stated above. Also it makes sense that the displaced air needs to go somewhere, just never thought of it. Prefer gravity fill but we’re learning.

One modification for you to consider. If you travel with a full water tank, you'll likely find that you will arrive at your destination about 2/3 full as the water tends to siphon out the overflow while travelling. Many install a ball valve on the overflow(s) that remain closed ONLY while travelling so that you dont lose water. Just have to make sure they remain open all the rest of the time so that you dont blow the tank up, or collapse it with vacuum.

I did this on my Cardinal, as I always travel to my local camping destinations that are not full hookup with a full tank. I despise sitting at the dump station filling at arrival.

TazFord wrote:
Thank you everyone. I was just leary of overfill after hearing stories of damaging RV’s. Now I know and I found them dangling by my drain plug as stated above. Also it makes sense that the displaced air needs to go somewhere, just never thought of it. Prefer gravity fill but we’re learning.

I also prefer a gravity fill but I've also found that it's much better to fill your tank =slowly=. I'm pretty sure that the first time I boondocked with my new KZ, which doesn't have a gravity fill, I managed to siphon out a goodly portion of my fresh water. I was filling and got a good flow out of the overflow but, even being as water-conscious as possible, we managed to run out of fresh water in just 4 days. I'm =supposed= to have 61 gallons, total, and I plan on getting a meter to check that I'm actually getting 61 gallons. Next time I have it at the house, I'm going to check, then drive around a bit with someone following me to see if I get any siphoning. Then, I'll measure what I get from the low-point drain. I've read more than once on here that people expect to have a tank of X gallons but end up with one that's X-10 or 15 gallons.

Lyle

Thank you everyone. I was just leary of overfill after hearing stories of damaging RV’s. Now I know and I found them dangling by my drain plug as stated above. Also it makes sense that the displaced air needs to go somewhere, just never thought of it. Prefer gravity fill but we’re learning.