RV Doctor – How Do I Link A Second Freshwater Tank in My RV?

author image

March 8, 2009

Dear Doc,

Like many people, we do a lot of dry camping. And one of the most important resources when dry camping is the water tank capacities. Unfortunately the new RV we just purchased only has a 50-gallon fresh water storage capacity. Not enough for a long weekend with our three kids. I’ve been told I can add an additional tank to increase that capacity. I’ve even found a site that sells RV water tanks of various sizes at reasonable prices. However, I have no idea how you would go about “linking” the new tank to the existing tank so I would only need one filler spout and one pump. Do you have any suggestions as to how I might do this?

Dave Chittum, (Newhall, CA)


Dave, installing a second fresh water storage tank is indeed doable, however, I usually recommend a separate fill to accommodate faster filling.

It can be done with a single fill by linking the two tanks together with an approved fresh water tubing. Both tanks must be on the same level and be the same height in order to get by with one fill spout. You’ll need to connect a water line, the larger the better, at the bottom of each tank and a vent line at the top of each tank, linking the tanks together.

Some tanks have auxiliary threaded fittings already installed, but additional fittings can be welded on or spun on by any properly equipped RV shop. There are even two-piece fittings available that simply require a hole drilled in the tank to install.

Leave the pump where it is and let gravity do the work of equalizing the levels in each tank. Remember, water seeks its own level, so if they are connected together at the top and bottom, they will drain together as water is pumped through the system. They will also fill at the same time, though it may take more time for the levels to equalize during the filling process.

You’ll only need barbed fittings and simple hose clamps since the new fittings will not be pressurized. Only those fittings located downstream of the water pump will be under any pressure other than static pressure. The hardest part will be routing the fresh water tubing between each tank. But it will indeed provide additional fresh water storage. Don’t forget, the new tank will also require its own drain valve and fitting as well.

(Please feel free to comment, however, please also note that due to the volume of communications I receive from multiple channels I cannot guarantee a personal response in every instance. However, questions of an overall general interest may be considered and published in an upcoming RV Doctor column.)

Leave a Reply


  1. Pingback: click here

  2. Pingback: accutane

  3. Pingback: sims 4 crack

  4. Don Ackerman

    I too, bought a 65 gallon ag tank. I carry it empty, and fill it just as I enter a dry camping area. It is mounted on a slide-in cargo rack on my reciever amd it strapped down. Set-up and pumping are the same, basically. I use my white water hose to pump to my tank with the filter in between. Works great, especially when you have extra women on board. If you overfill your greyblack tank using this or anyone’s suggestions, ya probably need to be hit in the head with a tack hammer for bad headwork. You need to pay attention!

  5. mark dowling

    When we first started dry camping with our 3 kids, we’d use up our 37 gallons of fresh water the first day. Since then, we taught the kids to make a game of saving water, we changed the way we did dishes and took showers and we switched to foaming hand soap. Now we can dry camp for 3 nights and still come home with half a tank of fresh water left.

  6. John Sage

    What happens when the RV floods because the gray water tank is full and you have 50 gals of fresh water left?

  7. David Humphrey

    I have a Anon 7.5KW diesel generator that refuses to start at temp below 40 degrees ( just clicks) but starts fine at higher temps no problems ?

  8. mark lutes

    I solved to need for more water by buying a 30 gallon agriculture water tank with the big fill cover . I attached a garden hose type shut off on bottom I put this tank in the front area of my pickup using a 2×6 slipped in the brackets in the box to keep it there. I attacked a washing machine hose to the tank and the I bought a 12 volt water pump with a garden hose connections. attaching the pump to the washing machine hose in the in side and a garden hose to the out side. that hose is then place to my fill on the RV. I power the pump with a 12 volt jumper box, or you could attach a wire to the hot line on your power plug. I can refill my RV in just a few minutes. If I need more water I can drive to a local water supply refill my tank and return to the RV with more. The tank clears my 5th wheel hitch so it will work with any trailer. Any questions feel free to Email me

  9. Fred

    I/we have a 75 gal. tank in the bed of our pickup and just run a hose from it to filler on trailer….gives us plenty of water.

  10. Cliff Thew

    The reader did not ID the type of RV he is using but if it is a 5th wheel he has a truck that has considerable carrying capacity. Personally for the amount of work vs the payback, I would purchase one or two of the bladders available to place in the back of the truck for extra water. A small 12v pump can be used to transfer to the RV’s fresh water tank. An added benefit is that you can take the truck to get more fresh water with ease which is not the case with a built in tank. There is even a bladder that you can place on a roof rack of the tow vehicle to give a gravity feed to transfer the fresh water. Remember, at 8.3 pounds per gallon, your auxillary tank had better be well supported to the frame or you will end up watering the macadam, so to speak

  11. bob

    Dont forget the added weight of all the water balance the load and dont go over what the rig can carry. bob