Here's a quick and cheap way to protect your parts washer tank from corroding. I've noticed the cheaper tanks require a water based solvent which are almost always acidic so here is an easy way to protect your tank from corrosive solvents.
Step one - Attach some copper wire to some scrap aluminum by using a steel bolt. Here I used a scrap piece of an old Stan's rim. I sanded it down a little so that the bare aluminum could be in contact with the fluid in my tank. In my case I use about 1 gallon of purple power to about 12 gallons of water. The acidity will only affect the consumption rate of the aluminum, the tank will be safe as long as you install a new piece of aluminum when the old piece gets consumed.
Step two - Attach the other end of that wire directly to the tank (inside or out, doesn't matter).
Step 3 - Submerge scrap aluminum inside the tank
That's it, you're done. The most important part is that the aluminum is electrically continuous with the steel in the tank and that the aluminum is placed inside the fluid.
Here you can see I measured the results using a CuCuSO4 reference cell. My native steel potential is about -593mV. Minimum protection is -693mV. With the aluminum anode I have achieved -1136mV which proves that the steel is easily being protected by the aluminum.
Native steel potential of the tank and reference cell for testing. This was taken before the aluminum was placed in the tank.
Now protected at -1136mV. This is after the aluminum was submerged in the tank. Note: this only works if the aluminum is somehow connected to the tank.