Filling Two tanks via fire hydrant

While I’m building my new trailer setup, trying to map out the best way I want to fill my (possible) two tanks. I already have a 300 gallon leg tank along with looking at getting a 500 gallon tank. I already have my way set up I am going to fill them (top fill with an air gap), but do I want to only fill one via the hydrant and have a 2-3" line connecting the two at the bottom? Or do I want to try to rig something up to top fill both of them? I don’t know if anyone has done this or you physics guys have any suggestions?

You will need a ball valve between the two tanks to shut off flow or else you will overflow the 300 gallon tank. We are building a custom set up right now similar to what you are talking about, there is one fill line that top fills both tanks with a 2" ball valve at the top and bottom connections so you can shut off tanks from each other. I can send you a picture on Tuesday if you would like.

Yes please! What size connecting line are you using? I would think I would need a 3" connecting line w/ball valve just to handle the high volume during fill up. When I had my other rig I could fill up a 525 gallon tank in under 2 min. I can’t see a 2" connector line equalizing the tanks fast enough or am I wrong?

You probably will need a larger hose, this particular system we are building is for use with a water transfer pump that produces about 160 gpm. Most your hydrants should produce significantly more. I will send you pictures on Tuesday so you have something to look at.

I appreciate it Trey

Use 3" pvc and make a swivel that can place the hydrant outlet at the fill hole of each tank, fill one, move arm and fill the other… just a thought.
You can connect the two tanks and fill one from the top, but that is not an exact science. I would connect with 3 inch if you were going to do that, it will equalize both tanks quicker than 2 inch. 800 total gallons is not alot when filling off a hydrant with 3 inch. My 1550 gallon tank fills in a few minutes with the 3 inch feed on my fleet washing rig.

Also remember most Cities require that you have 2x the distance between the water outlet and the top of your tanks for acceptable Air Gap.

Example…if you’re running 3" pvc to fill your tanks you will need a 6" separation in the outlet dropping in the tank and the top of your tank.