How to do plumbing to add a second fresh water tank

jeepbluetj · Mar 10, 2016

I'm not Ms. Hall, but I'll toss my $.02 in anyway.
Simple: just Y (or T) the two tanks together at a point that is lower than both of them. They'll empty highest to lowest that way. Whatever fitting type fits your tubing. (i.e. a barbed T for poly tubing, a pex T for pex, etc..) Of course the outlets of the tanks should be on the bottom of them.

Option: Add two ball valves between the tanks and the Y - so you can isolate a tank (so you don't run out unexpectedly or something)

Jackdaw · Mar 11, 2016

No, you are going to want to be able to isolate the two tanks. You don't want the water to transfer. This means you're going to need a manifold with a T-valve on each of the inputs from the tanks, being drawn on from a common output that is attached to the pump.

This picture shows more than two tank inputs, but you get the general idea. This should not be below the level of the tanks, it's better if it's above.

jeepbluetj · Mar 11, 2016

I'll disagree. Not completely, just a little.

The OP's Boat: Hunter 27. Guessin a coastal cruiser. Guessin if they lost all the fresh on board they'd just go get some more. No real need for a complex system. (Like when Catalina put two tanks in a c-30 - they were just plumbed together)

Completely different beast if you're offshore and/or have a watermaker. The 'value' of the potential fresh water draining into the bilge or the potential of the watermaker turning a tank brackish is far higher than for coastal folks.

I'm a big fan of KISS, and that there's horses for courses.

Jackdaw · Mar 11, 2016

jeepbluetj said:
I'll disagree. Not completely, just a little.

The OP's Boat: Hunter 27. Guessin a coastal cruiser. Guessin if they lost all the fresh on board they'd just go get some more. No real need for a complex system. (Like when Catalina put two tanks in a c-30 - they were just plumbed together)

Completely different beast if you're offshore and/or have a watermaker. The 'value' of the potential fresh water draining into the bilge or the potential of the watermaker turning a tank brackish is far higher than for coastal folks.

I'm a big fan of KISS, and that there's horses for courses.

Your boat your call. But I always look at upgrades to boat systems as a way to better the cheap shortcuts the builder took, and not replicate them.

Johnb · Mar 11, 2016

I would want to be able to isolate the tanks from each other so
1 You can fill one tank and then the other - assuming the fill would be much quicker than the cross draining and you want to get them full one at a time
2 If they are on opposite sides you don't want one draining to the other when heeled
3 They are independent and one is a reserve for the other.

Stu Jackson · Mar 11, 2016

Johnb said:
3 They are independent and one is a reserve for the other.

Yup, and you don't need a tank monitor. When one's empty, switch to the other and make a note to refill.

Peggie Hall HeadMistress · Mar 12, 2016

jfgy said:
I plan to add a second water tank to my Hunter 27. The installed tank is 20 gal, and another 12-15 would be very helpful. I'm looking at Ronco for a small tank that will fit. I

Have you tried to find a location for a larger tank instead of adding one? 'Twould be a lot simpler to plumb.

Peggie Hall HeadMistress · Mar 13, 2016

Since the built-in only held water, could you cut the top off and use it for storage if you can find a location for a larger tank?

Just a little "outside the box" brainstorming....