Curing Vacuum Truck Tank Corrosion & Collapsed Hoses

A freshwater tank is rusting from the inside and a PRO wants to know how to stop the damage.

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QUESTION: One of our trucks has a 250-gallon freshwater tank that is rusting inside, which is a problem when we have to fill sinks on a service route. There is only a 2-inch fill opening on top so we can’t get inside. Is there an additive or treatment we can use to remedy the problem or do we have to cut a trapdoor into the tank?

James Lavarone
Mill Valley, Calif.

ANSWER: You’re not the first portable sanitation contractor to encounter this situation.  When it comes to ensuring clean water, there is no quick fix when rust starts attacking carbon steel. Many freshwater tanks have been built with only a 2-inch fitting on top. Unless the tank is coated with an approved epoxy or is built from stainless steel, it is not possible to avoid rust.

Carbon steel, water, and air create an environment where rust will form. Rust causes discoloration of your freshwater supply and ultimately shortens the life span of your water tank.

I’ve known PROs who attempt to head off rust by pouring various chemicals into the tank, but there is no way to guarantee all interior surfaces are coated. I’ve heard the suggestion of replacing the 2-inch fitting with an 8-inch opening, the logic being that a technician could get an arm in and try to spray the interior with a rust inhibitor of some kind. Don’t waste your time.

In your case, the best thing to do is install a manway on top of the tank. With the opening big enough for someone to get inside, you could then be assured of coating the interior completely.

If you’re looking for reasonably “clean” water, you can coat the tank with a marine emulsion available at stores that sell paint and coatings. Sometimes cleaning the inside of the tank and applying a couple of coats of shop primer will do the trick to halt the progress of rust. However, remember this will yield “reasonably clean” water, not pure water.

You’re not done yet. If you’re trying to get a coating suitable for drinking water, the simple “trapdoor” won’t work. It most likely would be acceptable at wash stations, but for drinking water, a couple more steps are required.

First, understand you’ll need a carbon steel tank that is sandblasted and coated with an approved epoxy for drinking water. In an existing tank, this means opening the barrel of the tank by cutting off the head. At that point, you’d have access to sandblast the tank interior and coat both the tank interior and the head you removed.

Once the head is welded back in place, the weld seam must be protected. This is where the manway comes into play. A technician climbs in and coats the interior weld seam and you’re ready to haul drinkable water.

This process is time-consuming and expensive. The best time to remedy this situation is during construction of a new tank. The manufacturer can coat the interior with epoxy and install appropriate compartment access points.

Another solution is to find space on the truck for a separate 250-gallon stainless steel tank. Or replace the rusting tank with a new stainless steel tank. This allows for clean water, avoids rust, and – if built properly – the tank should outlast the truck you install it on. Stainless will cost more, but eliminate concern over rust.

The case of the collapsing hose

QUESTION: For some reason my vacuum hose keeps collapsing. It is good, steel-reinforced hose, but it’s causing problems on the job site when I’m pumping.

Shane Benson
Pierre, S. D.

ANSWER: Some vacuum hoses are composed of an inner skin, steel reinforcement and an outer skin. The inner skin is attached by use of an oil-based glue. This type of hose works fine for normal portable restroom work. So most likely your problem is that you’re pumping oil into your system and it is compromising the hose’s glue system. When that happens, the hose collapses on the inside and your pumping stops. There are solid rubber hoses with steel reinforcement available at most hose supply businesses. Explain your problem and they should be able to provide you the right type of hose.



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