PORTABLE WATER MOD

With a pair of 3-way valves (the type used for a water heater bypass) and a few plumbing fittings, you can configure the pump to fill the tank using the same line that it normally uses to draw water from the tank. One valve goes in the pump inlet line to connect a suction hose to the pump while blocking the tank output line, while the other goes in the pump outlet line to redirect the pump output to the tank outlet line, using it as an inlet. A switch mounted near the pump provides local pump control.

been doing this for almost 10 years and it works great. I have the 7 gallon blue square water jugs. I have a 30" long SS roughly 1/4" dia tube hooked to flexible water line to the pump inlet. then I took off the vent cap on the blue jug, drilled a hole in the vent the size of the 30" dip tube, angle cut the bottom of the dip tube. the extra pump is hard mounted in the pass through with the outlet hard coupled to the trailer tank water line.

normally the cap and vent cap are on the jugs. When I go to fill, I remove the caps, push the dip tube in the vent hole all the way to the bottom, turn on the pump. dip tube stays all the way to the bottom and I pump away.

I bought another pump, wired it with a 12v connector, fuse and switch, and put a 10 foot hose on each side. I stick one hose in the portable water tank, the other hose in the fresh water tank fill opening, plug in the pump and turn it on. Simple. I had already run 12v to that side of my RV to power my Flojet Macerator when dumping at home.

And, if my RV's water pump dies on a trip, I have a replacement right there.

After reading and re-reading your original post several times I've concluded that what you really want to do is use your existing on-board water pump to transfer water from a some sort of portable water container into the trailer's fresh water holding tank. It also seems your particular trailer has a conventional gravity fill fresh water port. Yes? :h

Assuming so, the simplest method is to run the pump's output to the trailer's gravity fill port but obviously if you want to use the existing on-board pump for this purpose you'd have to valve both the pump's intake and output so anyone else who might want to use the trailer's water system will have to wait 'til you're done. To avoid this I've always used a separate potable water pump for the task as doing so doesn't disrupt normal use of the trailer's water system at the same time. If you'd rather not have to run the pump's output hose to it's connection point each time you can plumb it permanently to one of the ports on the tank, just as I've done with our current trailer - 8 pics. No need to make it any more complicated than this. ;)

Bulletboy wrote:
Hey guys, I have a TT with a Flojet 2.9gpm pump. I want to use this to pump out a portable water tank,..through the vent hose.

Your post as written doesn't make a whole lot of sense to me :h ... are you saying you want to pump water out of your trailer's fresh water holding tank to empty it or to transfer fresh water from some sort of potable water container into the trailer's FW tank? :@

Thanks for your replies. My overflow is the vent and I was thinking the same as Scott...that my inlet could vent....just reversing the system basically. I have a 1 1/4" gravity fill line, a separate city water line, and a vent/overflow line, and a drain line.

Your water tank has at least three openings/connections. One is the outlet at the bottom that feeds into the pump. The second is the inlet for filling it, probably near the top but not essentially so. The third is the vent from the top of the tank. There may be an additional drain connection, too (if not, the drain is tee'd off the outlet), and possibly an overflow to prevent overfilling the tank—though the overflow could just be through the vent line.

There are a couple of different filler setups that are used. Some use a gravity fill, where the inlet for filling just goes straight to the tank. Others use the same external connection for city water hookup and for tank filling, with a fill valve to run the water into the tank. If you have the latter setup, your proposal probably won't work because there would be no vent for the tank as there's an anti-backflow one way valve at the city water inlet.

If you have the combined inlet and also a winterize suction line input, you likely can fill the tank using the pump already by setting the valves etc. for winterizing and opening the tank fill valve. If you don't have a winterizing setup, what you're proposing to install could very easily encompass one if you give it a bit of care. (You need to be able to switch the pump suction from the trailer tank to the external source independently of switching its output around for it to work for winterizing.)

As a general matter, I wouldn't suggest filling via the vent line. The tanks are not designed to be used under pressure, and should you forget to otherwise vent it, there's the possibility (but not necessarily a likelihood) of rupturing the tank or causing a leak.

Seems like the tank would need some way for the air volume to diminish as you pump water in. At a minimum you'll need to remove the filler cap to let air out.