Cleaning old gas out of a motorcycle tank


So, I’m going to be fixing up a couple of motorcycles, one to sell, one to keep. In both cases I’ve probably got partial tanks of old gas and I’m wondering what chemicals I should use to clean it out. Googling gives every result from soap and water to fresh gas to oxygen bleach to varnish remover (which would strip the paint, which is acceptable on one bike but not the other) and even phosphoric acid.

So, anybody who’s done something like this, I’m looking for effective, reasonably inexpensive, and preferably not ridiculously toxic.


Several commercial products, POR makes one I have used a couple of times. It won’t harm the paint from what I recall and I still had the OEM paint after the work was done. I removed the valve(s) and plug. If you have a lot of rust or buildup, some mechanical abrasion is helpful. I used small link chain put in with the chemicals and agitated by hand. A sealer can then be applied to prevent further rusting. Again POR makes a good product for this.


NOT soap and water! NOT bleach!!! Mineral spirits or kerosene are a good start. They won’t damage the paint. The bigger problem may be rust inside the tank. If that is the case, the bike will always have issues with flaking rust clogging up the filter.

If rust is the problem, phosphoric acid is a pretty good pickling agent to clean the rust. There are coatings that can be poured in to coat and seal the tank. Follow their instructions for prep. The tank’s paint is at risk. there may be no other choice.


Do you happen to have the name of this POR product?


Jegs has the kit here-

Here’s just the sealer-

You may be able to find better deals looking around.

Here’s the POR site-