I have been using two 4-position valves on my truck since I got it in about 1986-87.

Like http://https://www.amazon.com/Moeller-Fuel-Four-Way-Valve-Brass/dp/B000MTI18M/ref=sr_1_1?crid=DE2KIV0F8AAU&dib=eyJ2IjoiMSJ9.pS1DI6h6eWch_8ghpIJFEWoncXP_KrzUowWNcPW4K8O59UaE7PNTV8_dBJje5Y7sdRBfQj3iADIfpLTNX8Vt5EyyAf5I7IqdWUfqLw9zuAn2_cWJ2p_CfMY169OJC6XXuGdtPKRf1RSheN-IxcjmpkhhvFbT6s26PN_MH21pEeTJuxnD1AfROKh5jdBsE98x5HCjQTTdYs7r4ZA8SACYD8e0_Hn67ZYfT_M3rvSRIW3K9tX95TsUuzPv_dJV9BN1cdp8wyfg2rA862pb5DtwhlSbhAUIGWmpQ-YfmqWRgeQ._yekpeh0mk62AYvpa0neLc6MdiylAlvqUkv5CD4Gopo&dib_tag=se&keywords=Moeller+Four+way+valve&qid=1712845975&sprefix=moeller+four+way+valve%2Caps%2C2723&sr=8-1" rel="nofollow - THIS

Diesel, of course.

One valve is for DRAW and the other switches RETURN.

The plumbing is under the floor and a short stem pokes through the floor and a fancy plate and is topped off with a handle/lever with which one turns the internal ball valve from port to port.

The fuel outlet to the engine is straight out the bottom with the three tank inputs perpendicular to that; so, the "Ball", instead of being straight through like a plain old ball-water-valve, has a 90° fuel passage through it.

The bottom-facing passage always faces down and turning the handle points the perpendicular opening toward whichever input is chosen.

Of course, the fuel is travelling in the opposite direction on the Return Selector, but the principle is the same as the valves are identical. 

The four positions for either valve are OFF - Front 20-gallon factory tank - Big 52-gallon Auxilliary - Rear 20-gallon factory tank

Over the years, I have mostly used WeatherHead valves mixed with a few others, including Everco.

Hard for me to believe; but, I have not as yet dissected one of these valves to see whether the ball is plastic or the ported housing it rides in is plastic.

The main problem I have always had with all these valves is that the diesel fuel swells the plastic inside and the handle/stem gets tighter and tighter until one day it just snaps off in your hand, leaving you wondering did it switch tanks before snapping, or is it still on the empty tank, or is it lodged somewhere in between.

This is real handy when going around the bypass in Atlanta with a big load of cattle --- had that happen once about thirty years ago.

My question is = is there such a thing as these valves that are not affected by diesel fuel ?

Surely such exists as I have plain old hardware-store Ball-Cut-Off Valves where diesel has been running through them for years and they never seize up like these tank selectors do.

The ones on my truck now are warning me of their impending doom and I would like to have replacements on hand that will not be a repeat performance of the many I have had over the years.

I don't think I have ever tried a Moeller, like the one I linked to as example; maybe their internals are better suited for constant submersion in diesel.

Even considering the occasional stem snapping off, these manual valves are way far and ahead of any electric valve I have ever used --- I will never waste my money on another electric tank switching valve.

However, other than the poorly rated el-cheapos, Moeller is the only brand I can find available; a few years ago, there were at least five recognized brands making these.

I have driven countless old gas-burner two-tons with a tank in the cab behind the seat and a big tank on the frame under the door, some even have big tanks both sides, and always one of these valves poking through the floor to switch from tank to tank.

Most all of these old trucks are purpose-built seasonal-use trucks that sit for eleven months and are used heavily for maybe a month, then parked again.

Gasoline must not have any effect on the valves as they work just as good on a fifty-yr-old truck as they did when new.

I wonder if new "guts" can be had to replace the offending plastic part that swells up.

If I were to take one apart and maybe put some valve-lapping compound on the ball and work it to and fro a couple million times, maybe it would free up and be good for another several thousand miles.

One thing I learned pretty quick on the trucks with saddle tanks on both sides and that draw from both simultaneously is you had better know where the tank cut-off valve is and close it if you park somewhere where one tank ends up higher than the other and they are half or more full; the higher tank will over-fill the lower tank and the extra will run out on the ground.

On these trucks, they actually only draw from one tank and the fuel levels off via a crossover.

Anything newer than 05 no longer has a Cross Connect line, standpipe feeds from each tank to a T to the Engine, as one draws low the other has a higher available flow rate so starts feed from that one, return is done with a similar connection but thru a demand flow valve.  All Black magic Voodoo but will not cross feed sitting off angle.  Drain one tank to where the fuel standing in the standpipe gains weight to the fuel in the other tank will syphon feed to a point but not very fast.  My KW has that style System.  

https://www.fleetpride.com/parts/velvac-fuel-valve-060070" rel="nofollow - Velvac 1/2" FPT Return Fuel Flow Splitter for Ford / Kenworth 060070 | FleetPride

My dad had 75 GMC 2500 and added a 100 gal tank in the bed, as he pulled a 20 foot cattle trailer a lot. Everything was great. In 82 he bought a new truck, moved the 100 gal tank. Then the fun began. Thankfully never with a full load of cows. Running on the big tank with no fuel gauge you watch the regular tank gauge getting fuller. But all the worthless mechanics the dealer had had no idea of what the problem was.

I don't know if it was all trucks or just the California pollution compliant ones. The new vapor recovery system sucked extra gas and dumped the vapors from a carbon canaster into the gas and then sent it back to the tank. So if running a axillary tank the extra gas went to the regular tank and over filled flooding the whole system out. If you did not start using out the regular tank in time. And my dad being somewhat suborn, just ran his big tank for years, with the by passed gas going back to it. To have bought the electric toggle switch GM used on the trucks they put 2 tanks would have been way to easy. 

I think what you want is a '4 way stainless steel ball valve' ?

or maybe a 5 way ??

What I use is 4-way with positions OFF - Tank 1 - Tank 2 - Tank 3

I have determined that the problem is that the plastic that the ball pivots inside is not completely compatible with diesel fuel.

When I mount a brand-new valve, I can turn it with all ease from position to position.

No matter how often or how little it gets used, as time goes by, being constantly in contact with diesel fuel, the plastic swells and tightens against the stainless ball, making it harder and harder to turn.

The 1975 truck did not have a fuel return line; the 1982 most likely did.

I have driven and even owned a few trucks that had big auxiliaries and no means incorporated for a return line to the big tank(s).

On those trucks, you run the little tank until the engine stalls out and switch over to the big tank before the truck quits rolling; then, you run on the big tank and keep an eye on the little tank gauge; when the little tank nears Full, switch back over and run on it and rinse and repeat.

This plan works sort of okay with a gas-burner as you don't leave a gas-burner run while you are at a big sit-down dinner with desert; with a diesel truck, it is a constant recipe for disaster and plenty of fuel pouring out on the ground because you went away and forgot to switch and let the engine draw from the little tank.

Hence is why I have two identical valves; one for Draw and the other for Return.

Yes Yes, I know they make big long double valves that switch both, Draw and Return; try one for a while and you will see why I don't use them.

I'd get a true stainless steel selector valve as it'll have a SS ball.

google can help, as you know what 'connections' and line sizes .