If it’s not broken don’t fix it! Some things are better left undisturbed. Your vacuum tank manway that hasn’t been opened in 10 years is probably one of those things. Some tank entrances, such as your larger rear vacuum tank manway, may need to be opened on a weekly basis for proper cleanout. Once you have opened it, here are a couple of things to keep in mind.
Various components may need to be replaced when you try to open the manway. Wing nuts and bolts can be rusted and brittle after years of corrosion. Consider replacing them; this can save a lot of frustration and will help provide a secure seal.
Your vacuum tank manway gasket is the most important thing to check. Visually inspect the rubber gasket, and if in question use a flat head screwdriver to carefully pry it out. Check it for dry rot, tears, cracks or debris. You can use a hand held wire brush to remove heavy debris from your gasket. If you need a new gasket you can order it by the foot or as a specific size. When ordering rubber by the foot, be sure to order enough material so that when you install it the ends meet snugly. A gasket sealant compound should be applied at the joint to bond the two ends. Use of some grease all the way around will help the gasket install easier, enable the tank to seal better and provide corrosion resistance.
Older manways have the gasket installed in the neck. The newer styles usually have the gasket in the lid. Either way, be sure to visually inspect the metal surfaces that contact the gasket. If they are rough from rust or corrosion, you can use a wire brush or grinder to restore the smooth surface. If the rust is significant you may need to have a completely new manway installed.
If you do not hear your manway hissing when you run your vacuum pump, and if it is not leaking fluid, then you probably do not need to do anything to it. If you do open your manway be certain you get a proper seal when you close it. These simple procedures can help your tank perform better and save frustration and money over the long haul.