Fittings for potable water tank

[jbeech]

What are the typical fittings installed on the potable water tank?

I figure I need three fittings, a fill, an overflow, and a drain. Are 3/4" NPT typical, or something different. Any other fittings I should consider? Anyway, this is the tank I am planning on purchasing:

135 Gallon Rv Water Tank - RVB407

. . . and advice would be welcome. Anyway, I figure the pump is connected to the drain fitting on the bottom, and an overflow fitting (possibly two, one to each side of the truck), plus a third fitting for filling the tank via a water hose.

Thoughts?

[bushpilot]

this might help give you some ideas of the plumbing / fitting sizes -

RV Gravity Water Fill Hatch from PPL - PPL Motor Homes

[hot rod]

The tank on my trailer is probably far from a "standard" installation, but may be helpful. The service fitting to withdraw water comes directly out the bottom so no water can be trapped in the bottom when you drain it. I don't remember if it 1/2" or "3/4" female pipe, but it doesn't really matter, all I did was use a fitting to adapt from the threaded fitting down to 1/2" pvc anyway. I suppose it is easier to reduce it down than have it too small, so err on the big side. I used the schedule 40 pvc pipe, which they tell me you're really not supposed to use for drinking water, as I figured it is heavier and would be less likely to crack and we really only use the water for the sink and toilet anyway.

The fill is just a hose barb the same size as the hose barb on the fill door like what Don suggests, I have the same setup. I would suggest buying your fill door first, and match that fitting to the one you are going to have installed in the tank.

The the city water connection on the fill door just plumbs into your water system downstream of the demand pump, no big deal there. I would put the city water connection in while you are doing the system, whether you think you will use it right now or not. I didn't the first time, then when we decided to stay in campgrounds from time to time I had to go back and buy a new filler door and redo everything. Way easier to do it right up front.

And there is a smaller hose barb built into the tank along side the filler, again the same size as the hose barb for the overflow on the filler door. Just match that up as well. The overflow also serves as a vent.

[Bob86ZZ4]

I think you also want to put a one way valve on the out line from the tank. That way/in you hook up to city water it won't allow water to push back into the tank. That's how mine was set up. They also put a t-fitting in the out line from the tank. That t then has a shut off valve on it and leads down through the floor toward the pavement. Works great when I want to drain out the tank.

[jbeech]

Are the fittings molded-in, or are they a bulkhead type fitting? E.g. bore a hole, clean the flashing, and screw the pieces together with a gasket in between.

[Doc Weaver]

I'm busy on a out of town gig, but I wanted to add to vent it well. Mine is not and it takes forever to fill because of the trapped air trying to bubble back through the hose. I like Bobs idea. I may have to change mine over to like his.

[hot rod]

The fittings on my tank are bonded. To use a bulkhead fitting you'd need some sort of opening to reach in and hold the backside to tighten it together. But I did see a port like that on the website that jbeech referenced above if you wanted to go that way.