Siphon Action Draining Water Tank - Problem Solved!

[dagraf]

If the tank was not collapsing . . . how did a 2/3 level get up to the vent/overflow at the top of the tank? Perhaps trusting the tank level indicator is part of the problem. They are notorious for being inaccurate.

Rob

I was guessing that the vent tube sticks down into the tank a bit—perhaps you know different having pursued this issue. I can’t see how the tank could have collapsed at all with the gravity feed open.

I didn’t want to disparage the level sensor, but fair point. It did seem that the draining continued for a long enough time to be consistent with what the sensor indicated.

Thanks again for all the time you’ve put into this!

[TedS]

Freshwater tanks are generally wide and flat. If the vent connection is on the side and 2" from the top and the tank is only 7" tall the remaining volume would be 5/7(.71), nearly 2/3(.67).

[Cate&Rob]

The Parts Lookup section of the Grand Design website does not show the tank fittings on the drawing for the 2022 Imagine XLS 17MKE that dagraf has. But, a similar Imagine tank shows the fittings to be on the top surface. Even if the vent fitting was on the side of the tank, drawings of that configuration show the vent to be as close to the top of the tank as possible and would break the siphon vacuum as soon as the water dropped below the top of the fitting. Within 1" or less from the top of the tank. To get to a true 2/3 level while still siphon draining means that the tank has to be contracting in volume.

Rob

[TedS]

If the vents are truly on the top, there can be no siphon, only overflow. Especially with a gravity fill. Perhaps the sensors are misplaced or the tank is not level.

[dagraf]

Thanks, gentlemen. I will be moving the trailer around a couple times in coming days so I will fill ‘er up, drive around a bit, and see what the measuring bucket tells me. Will report back if I learn anything.

[mtd1899]

Still happening
I have a 2023 17mke
It loses 1/3 tank of water on a interstate highway drive.
On a 200 mile Montana back road drive it lost 2/3 of the water
Ideas?
It has 2 vent hoses, water comes out ofbboth

[acoleman43]

Still happening
I have a 2023 17mke
It loses 1/3 tank of water on a interstate highway drive.
On a 200 mile Montana back road drive it lost 2/3 of the water
Ideas?
It has 2 vent hoses, water comes out ofbboth

Same thing would happen to us. We'd fill up fresh tank to get ready for a week or more of boondocking, but by the time we reached our destination, 1/2 the water was gone.

I cut the overflow about 6" shorter, went to Home Depot and installed one of these at the end of it. I keep it open unless I fill the fresh tanks and to go boondocking. Has worked great for me.

[Jlawles2]

I did similar before the "fix" came out by using https://www.homedepot.com/p/SharkBit...V22A/324634591 since it did not require special tools to install and remove at a later date.

I do keep the valve closed along with the drain due to our "flying critters" that like to make mud nest in strange places.

[Cate&Rob]

Still happening
I have a 2023 17mke
It loses 1/3 tank of water on a interstate highway drive.
On a 200 mile Montana back road drive it lost 2/3 of the water
Ideas?
It has 2 vent hoses, water comes out ofbboth

As described at the start of this (now very long) thread, the dual overflow system should stop water flow in a static situation. In other words . . . after you fill to overflowing, the overflow will stop. This was not the case with the single overflow tube. What you are experiencing is “slosh pumping” while driving. Nothing can stop this except the described valves, if your drive includes rough roads or a lot of stop and go.

If you have an external gravity fill port, this should also provide an air path for escaping air when pressure filling or air to be drawn in when using water from the tank. Many Grand Design products do not have this provision so owners of these must be very careful with the operation of valves added to the overflow/vent.

Rob

[Country Campers]

It is also worth noting again that the fresh water tank is only to be filled until the full light is indicated on the convenience panel. This is below the overflow pipe and will leave a air pocket at the top of the tank.

Brian

[TucsonJim]

It is also worth noting again that the fresh water tank is only to be filled until the full light is indicated on the convenience panel. This is below the overflow pipe and will leave a air pocket at the top of the tank.

Brian

My light was horribly inaccurate. I gave up on it. Here's how I fill..

1. Empty the holding tank completely and close the dump valve.
2. Attach a flow meter to the fill hose.
3. Fill the tank to approximately 5 gallons less that it's published capacity.

Jim

[acoleman43]

My light was horribly inaccurate. I gave up on it. Here's how I fill..

1. Empty the holding tank completely and close the dump valve.
2. Attach a flow meter to the fill hose.
3. Fill the tank to approximately 5 gallons less that it's published capacity.

Jim

Just fill it until it comes out of the overflow